32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOYA001

B. X. Han†, R. F. Welton, C. M. Stinson, V. J. Andzulis, G. P. Terszakowec, C. Piller, S.-H. Kim
Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, TN, USA
Abstract-

The performance of the SNS H ion source was significantly improved over the years with a primary emphasis on
operational lifetime and reliability. The recent developments in support of the SNS Proton Power Upgrade (PPU)
have resulted in a remarkable boost in the ion source output
current, increasing from the existing capability of ~60 mA
to more than 100 mA. This paper briefly reviews the ion
source reliability improvements and discusses the designand diagnostics of recent beam current enhancement.

INTRODUCTION
The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is a large-scale accelerator-based pulsed
neutron facility. The accelerator system of the SNS includes a 65 keV injector, a 2.5 MeV RFQ, a high energy
Linac chain (warm Linac + superconducting Linac), and a
proton accumulator ring. The injector consisting of a H- ionsource and an electrostatic LEBT provides H- beams withthe required current intensity and time structure for the
SNS operation. SNS has recently undertaken a major upgrade to double the proton beam power from 1.4 MW to
2.8 MW, which involves Linac beam energy upgrade from
1.0 GeV to 1.3 GeV, Linac beam current increase from
~35 mA to ~50 mA, and a reduction of chopped beam fraction. The SNS H- ion source reliably supported the SNS
1.4 MW operation in the past couple of years with ~55 mA
beam current operating at 6% duty-factor (1.0 ms, 60 Hz)
covering 3-4 months long SNS run cycles. This establishedperformance of the ion source could reach the requirements
set forth by the new beam power goal. However, it is essential to have a sufficient beam current margin to allow
operational flexibility and reliability.

The 2 MHz RF is capable of operating at 60 Hz with 1 ms
pulse length and a power level up to 80 kW for high-density plasma generation. To facilitate fast and reliable ignition and buildup of the 2 MHz high-density plasma pulses,
a low-density background plasma is generated and maintained in the same chamber with a continuous, low power(~300 W) 13.56 MHz RF applied on the same antenna. A
pair of rod magnets provide plasma filtering for creating a
low electron temperature plasma region favorable for Hformation. A solid reaction Cs dispenser system(Cs2CrO4 + Zr, Al) is used for ion source cesiation. A Mo
cone located near the ion source outlet aperture enhances
H- yield through negative ion conversion on its properly
cesiated surface area. The co-extracted electrons are separated from the H- beam and dumped on the e-dump electrode by a transverse magnetic field generated in the ion
source extraction region by an array of magnets that areembedded in the outlet electrode. The extracted H- beam iscoupled into an electrostatic LEBT which transports andinjects the beam to the RFQ.

THE SNS H- ION SOURCEThe SNS ion source is a multicusp-confined, RF-driven,
Cs-enhanced H- ion source. This type of ion source wasdeveloped at Lawrence Berkeley National Laboratory(LBNL) initially for the Super-conducting Super Collider
project and then for the Spallation Neutron Source projectin 1990s and early 2000s. Since the ion source was operated at SNS starting in 2002, it has been further developed
for long lifetime (several months), highly reliable, persistent high current (up to 60 mA) H- beams for 1.0 ms pulses
repeating at 60 Hz [1-9]. Figure 1 shows a cutaway viewof the SNS H- ion source with its key components denoted.
The ion source plasma is driven by a 2 MHz RF through a
porcelain-coated, water-cooled copper-tube RF antenna.
____________________________________________* Work supported by UT-Battelle, LLC, under contract DE-AC0500OR22725 with the US Department of Energy (DOE)† Email: hanb@ornl.gov
MOYA: Main Session MOY
MC1.2 Electron and ion sources, guns, photo injectors, charge breeders

Figure 1: A cutaway view of the SNS H- ion source.
The significant improvements which have contributed tothe high-performance ion source operation include: Quality improvements of antenna coating (material
composition, layer thickness, and rigorous inspection)
allowing the ion source lifetime extension from theoriginal 2-3 weeks to >4 months.
 RF systems improvements (relocation of RF amplifiers from ion source high voltage deck to ground potential, frequency shift and amplitude modulation at thestart and end of the 2 MHz RF pulses, optimization of
13.56 MHz RF matching) enhancing the ion source
plasma ignition and operational reliability.

MOYA001
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BREAKING THROUGH 100 mA H- ION SOURCEOUTPUT CURRENT AT SNS*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOZA002

Oksana Chubenko∗ , Northern Illinois University, DeKalb, IL,USA
Abstract
Due to their key properties, photoemission-based electron
sources (photocathodes) are now widely used to generatebright and spin-polarized electron beams for advanced accelerator applications. The performance of these applications
is limited by the quality of the photocathodes. Therefore, research and development of high-quality photocathodes withsuperior brightness and, where required, spin-polarizationthat can endure realistic photoinjector conditions is crucial.
This paper will cover some of the latest advancements in photocathodes for generating bright and spin-polarized electron
beams.

INTRODUCTION
Cutting-edge electron accelerator applications, such as
X-ray Free Electron Lasers (XFELs), Ultrafast Electron
Diffraction (UED) and Microscopy (UEM), as well as particle colliders including the Electron-Ion Collider (EIC),
require high-quality electron beams. The quality of electron beams is characterized by their brightness. To enhance
beam quality, it is essential to understand the factors that
limit brightness. For high-charge-density applications, one
key limitation of the 4D brightness 𝐵4𝐷 is the accelerating
electric field ℰ at the photocathode surface, which determines the maximum charge density that can be extracted
without degrading brightness
ℰ𝑛
𝐵4𝐷 ∝
,
(1)
𝑀𝑇 𝐸
where 𝑛 varies between 1 and 2, depending on the photoinjector design. Another critical factor is the mean transverse
energy (MTE) of the photoemitted electrons. MTE is defined as the average kinetic energy of emitted electrons in
the direction perpendicular to the beam propagation. Due
to different effects, the MTE of electrons emitted from conventional photocathodes is limited to several 100s of meV,which is nearly an order of magnitude larger than the theoretically predicted MTE limit (𝑀𝑇 𝐸 min ≈ 𝑘 𝐵𝑇 ≈ 25 meVat room temperature, where 𝑘 𝐵 is the Boltzmann constantand 𝑇 is the temperature). Typical factors that limit MTE
include the requirements for high charge density, the disordered nature of photocathode materials, surface roughness,
and work function variations.
For high-energy-physics and nuclear-physics experimentsthat rely on spin-polarized electron sources, it is importantto have very high electron spin polarization (ESP), which
is defined as the degree to which the spin is aligned with agiven direction and is given by𝑁↑ − 𝑁↓𝐸 𝑆𝑃 =,(2)
𝑁↑ + 𝑁↓∗ chubenko@niu.edu

MOZA: Main Session MOZ
MC1.2 Electron and ion sources, guns, photo injectors, charge breeders

where 𝑁↑ and 𝑁↓ is the number of electrons with spins parallel and antiparallel to the direction of beam propagation,
respectively. The ability of photocathodes to generate spinpolarized electron beams stems from the unique band structure of the photocathode materials. The maximum achievable ESP in experiments is determined by fundamental scattering mechanisms within these materials.
The overall quality of a photocathode is described by its
quantum efficiency (QE), which is defined as the ratio of thenumber of emitted electrons 𝑁𝑒 − to the number of incident
photons 𝑁ℏ𝜔
𝑁𝑒 −
𝑄𝐸 =
.
(3)
𝑁ℏ𝜔
Photocathodes with higher QEs can produce electron beams
with higher intensities.
Many applications require photocathodes with a prompt
response time, which refers to the time it takes for a photocathode to emit electrons in response to incident light. The
response time depends on the material’s electron escapetime, which is the time required for photoexcited electrons
to reach the surface and escape into the vacuum.
It is also important to have a robust photocathode withlong operational time, which means that photocathodes must
operate under realistic photoinjector conditions. The photocathode reliability and stability under high electric-fieldloads and large laser fluences are crucial for sustained experimental operations.
Evidently, the quality of the electron beam is directly
limited by the quality of the photocathode. Detailed theoretical photoemission modeling, combined with advanced
photocathode characterization techniques, can be utilized
to improve the performance of traditional electron sourcesand develop new ones with enhanced capabilities. Here, wewill review some theoretical and experimental approaches
towards generating high-quality electron beams for brightand spin-polarized applications.

PHOTOCATHODES FOR BRIGHT-BEAM
APPLICATIONS
Traditionally, many accelerator facilities use metallic photocathodes to generate electron beams. Operating metallic
photocathodes with photoexcitation energy close to the photoemission threshold results in low MTE but also yields low
QE. While QE can be enhanced by increasing the photoexcitation energy, this also leads to an increase in MTE. For
high-current, high-brightness applications, photocathodes
can, in principle, operate near the photoemission thresholdunder high laser fluences. However, recent theoretical [1]and experimental [2] studies have shown that non-linear processes, such as multi-photon absorption, limit the MTE ofelectrons photoemitted from Cu to several hundred meV.
MOZA002
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STATE-OF-THE-ART PHOTOCATHODES FOR BRIGHT-BEAM AND
SPIN-POLARIZED-BEAM GENERATION

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOAA001

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THIN GOLD LAYERS ON NIOBIUM FOR SRF CAVITIES∗
S. Seddon-Stettler† , M. Liepe, T. Oseroff, N. Sitaraman
Cornell Laboratory for Accelerator-based ScienceS and Education (CLASSE),
Ithaca, New York, United States
V. Do, H. Lew-Kiedrowska, S. J. Sibener, University of Chicago Department of Chemistry
and James Franck Institute, Chicago, Illinois, United States
C. Wang, National Cheng Kung University, Tainan, Taiwan
Abstract
New materials beyond the standard bulk niobium havethe potential to greatly improve the performance of Superconducting Radio Frequency (SRF) cavities. Specifically,
thin coatings of non-oxidizing normal conductors such asgold have the potential to improve the key RF performance
metric of quality factor. We present progress on depositing
thin gold layers onto 2.6 GHz SRF cavities and testing their
RF performance.

INTRODUCTION
Superconducting Radio-Frequency (SRF) cavities underlie current cutting edge accelerator technology on a varietyof scales. Typically, SRF cavities are manufactured frombulk niobium, several millimeters thick, and are given a variety of chemical and thermal treatments to improve theirperformance [1]. Though the niobium is thick, the RF field
excited in the cavity interacts with the cavity most strongly
at the surface, specifically within (approximately) the first
40 nm [2]. Because of this, engineering and optimization of
the surface of niobium has become a strong focus of researchand development for improving SRF cavity performance [1].
When exposed to atmosphere, the surface of niobium
forms a complex, multi-phased oxide [3, 4]. By volume,the oxide is composed primarily of the pentoxide, 𝑁𝑏2 𝑂5 ,then lower phases including 𝑁𝑏𝑂2 , 𝑁𝑏𝑂, and other lower
phases. The pentoxide can be removed by thermal treatments at reasonable temperatures, but not the lower phases[5]. The electronic properties of the oxide, and therefore its
interaction with RF fields, are affected in many subtle ways
by different cavity treatments. The lower phases of the oxide
may have some normal conducting properties [3], which
may inhibit cavity performance at energies relevant to accelerator applications. However, due to the complexity andirregularity of the oxide, it is difficult to study in isolation.
Work at Cornell University and elsewhere proposed toremove the oxide entirely, then replace it with a thin layer ofa non-oxidizing normal conductor such as gold [6–8]. That
work showed promise for improving cavity RF performanceat very thin (sub-nm) layer thicknesses of gold.
∗ Work supported by U.S. National Science Foundation under Award PHY-

1549132, the Center for Bright Beams, the U.S. Department of Energy
under Award DE-SC0024137, and the NSF Materials Research Scienceand Engineering Center (MRSEC) at the University of Chicago, Grant
No. NSF-DMR-2011854.
† sgs238@cornell.edu

We have previously presented preliminary work towards
developing a gold passivation technique that could be applied on a full-scale SRF cavity [9, 10]. Here we discuss
progress towards a fully plated 2.6 GHz SRF cavity, including progress on the electrodeposition process and development of a suitable cavity.

ELECTRODEPOSITION OF GOLDA major challenge of applying a thin layer of gold to an
SRF cavity is the choice of deposition method. Many deposition methods common to materials science applications
are not able to accommodate the large size and irregular
geometry of a typical 1.3 GHz SRF cavity. Furthermore,
removal of all oxide layers requires a chemical treatmentof hydrofluoric acid in an inert atmosphere in order to prevent the oxide from reforming. Given these requirements,
we are developing an electroplating system capable of depositing thin layers of gold on niobium substrates that canbe performed entirely within an inert atmosphere glovebox[10].
Our electroplating setup uses a commercially available
sodium gold sulfite electroplating solution, which has a deposition rate that scales linearly with current density. Deposition thickness in electrochemical processes also scales
linearly with time. In order to deposit very thin films ofgold, we have developed a custom timing circuit that canreliably deliver very low quantities of current over very shortintervals of time [10]. During the process, the current ismonitored using an ammeter and recorded digitally, resulting in a trace of current vs. time. An example such traceis shown in Fig. 1. This together with the geometry of thesubstrate receiving the deposit allows for estimation of thedeposited thickness of gold.

SAMPLE CHARACTERIZATION
Optimization of an electroplating process for use on an
SRF cavity requires regular characterization of the films
produced by the process. There are two main tools for this:
X-Ray Photoelectron Spectroscopy (XPS), which scans overbinding energies to identify elements and chemical phasespresent on a sample, and Scanning Electron Microscopy(SEM), which allows for visual characterization of depositedfilms. An example XPS scan of a thinly plated niobium
sample, showing the presence of gold but with very low
counts per second (indicating a very thin film of gold), isshown in Fig. 2.

MOAA001

MOAA: Monday Oral Posters

10

MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOAA002

A. Gonzalez∗ , A.S. Plastun, P.N. Ostroumov
Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI, USA
Abstract
The linear accelerator at the Facility for Rare Isotope
Beams (FRIB) at Michigan State University uses a thin liquid lithium film for charge stripping of high-intensity heavy
ion beams. Energy straggling and energy loss of the beamin the inherently non-uniform lithium film affects the energy distribution in the beam. This can lead to non-linear“tails” in the longitudinal phase-space beam distribution
after bunching at the two 161 MHz room-temperature MultiGap Bunchers (MGBs) between the stripper and the next
accelerating segment. Some particles in these “tails” arelost in the downstream accelerator cryomodules. To mitigate
these losses, we have designed a room-temperature IH-typebuncher cavity with a resonant frequency of 322 MHz, thesecond harmonic of the MGBs. The new harmonic cavities will be installed next to each MGB, linearizing the
waveform of the effective bunching voltage and eliminating
the formation of non-linear “tails.” The increase in the energy acceptance of the post-stripper part of the accelerator
reached over 50% according to our simulations. We present
the electromagnetic design of this cavity along with beam
dynamics simulations that demonstrate how the losses are
mitigated. The construction and installation of the cavity
are being pursued as an accelerator improvement project.

INTRODUCTION
The FRIB linear accelerator is a state-of-the-art superconducting heavy ion linear accelerator. As shown in Fig. 1,
the accelerator contains three linear accelerating segments
and two 180 degree bending sections. For more efficient
acceleration, a charge stripper is located after the first accelerating segment (LS1). Two options are available for charge
stripping: a carbon foil for low intensity beams, and a thinliquid lithium film for high intensity beams [1]. Downstreamof the stripper, we use two 161 MHz Multi-Gap Bunchers(MGBs) [2] to keep the beam longitudinally bunched before
entering the second accelerating segment (LS2). Figure 2
shows a zoomed-in view of the layout between the stripper
and the entrance to LS2.
When the lithium stripper is used, energy straggling, energy loss and non-uniformities in the film cause a large energy spread in the beam after the stripper. This means thelongitudinal beam size is large when the beam arrives at thefirst MGB (MGB01). The large longitudinal beam size leads
to non-linear "tails" in the longitudinal phase space distribution after the beam experiences the sinusoidal 161 MHz
effective bunching voltage at MGB01. Particles in these"tails" are lost in the LS2 cryomodules. The lost fractionof the beam does not exceed 10−4 , which corresponds to∗ gonzalea@frib.msu.edu

MOAA: Monday Oral Posters
MC3.2 Ion linac projects

a temperature increase of up to 0.3 K in the beam pipe in
the LS2 cryomodules during 10 kW beam power on target
operation [3]. As beam power ramps up to our ultimate goalof 400 kW [4], the temperature increase in the cryomodules
will also ramp up, which may lead to degradation of SRF
cavities due to field emission. Therefore, it is necessary to
mitigate these losses.
Beam dynamics studies showed that the losses can beeliminated if the MGB effective voltage is linearized. To dothis, we have designed a Second Harmonic Buncher (2HB)
cavity to be installed downstream of each MGB as seen in
Fig. 2. This new cavity will have a resonant frequencyof 322 MHz, which is twice the resonant frequency of the
MGBs. The effect of this second harmonic is shown in Fig. 3.
The effective bunching voltage waveform of the combined
harmonics, shown in orange, has a significantly longer linear
region than the waveform of the 161 MHz MGB only.

BEAM DYNAMICS
We used the particle tracking code TRACK [5] to simulate
the effect of the new cavities on the beam dynamics. First, we
examined the effect of building only one 2HB and installingit downstream of MGB01 versus the effect of building two
2HBs and installing them downstream of each MGB. We
simulated the longitudinal acceptance from the lithium stripper to the end of LS2 for three cases: no 2HBs added, one
2HB added downstream of MGB01, and two 2HBs added:
one downstream of MGB01 and the other downstream of
MGB02. The results can be seen in Fig. 4. From theseplots, it is apparent that while installing one 2HB leads to asignificant increase in energy acceptance, the highest energy
acceptance is achieved when two 2HBs are installed.
The linearizing effect of the second harmonic can be directly seen in Fig. 5. To clearly demonstrate the effects of
the new cavities, we created an artificial beam distribution
with an exaggerated energy spread at the stripper and simulated it with TRACK from the stripper to the entrance ofLS2, taking snapshots of the longitudinal distribution at theexit of 2HB1 and 2HB2. In the top plot, when 2HB1 is on,
there are much fewer particles in the non-linear "tails" on theedges of the beam distribution compared to the case when
2HB1 is off. In the bottom plot, the distribution with thelargest linear region is when both second harmonic bunchers
are activated. In Fig. 6, it can be seen that when both 2HBs
are activated, all particles in the simulation fit inside thelongitudinal acceptance of LS2, whereas some particles arelost in the other cases. This further validates the decision tobuild and install two 2HBs.
MOAA002
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MITIGATION OF LONGITUDINAL BEAM LOSSES IN THE FRIB LINAC

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOAA003

J. Zhai†, W. Pan, F. He, R. Ge, Z. Mi, P. Sha, S. Jin, R. Han, Q. Wang, H. Lin, Z. Zhang,
M. Li, M. Sang, L. Sun, T. Zhao, B. Liu, X. Yang
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
Abstract
World’s first 1.3 GHz cryomodule containing eight
9-cell superconducting radio-frequency (RF) cavities
treated by medium-temperature furnace baking (mid-Tbake) was developed at the Institute of High Energy
Physics (IHEP), Chinese Academy of Sciences. The 9-cellcavities in the cryomodule achieved an unprecedented highaverage intrinsic quality factor (Q0) of 3.8 × 1010 at 16
MV/m and 3.6 × 1010 at 21 MV/m in the horizontal test.
The cryomodule can operate stably up to a total continuous
wave (CW) RF voltage greater than 193 MV, with anaverage cavity usable accelerating gradient of more than
23 MV/m. The results significantly exceed thespecifications of Circular Electron Positron Collider(CEPC) and Dalian Advanced Light Source (DALS) andthe other high repetition rate free electron laser facilities(LCLS-II, LCLS-II-HE, SHINE, S3FEL etc.). This
contribution reviews the cryomodule performance anddiscusses some important issues in cryomodule assembly
and testing.

INTRODUCTION
High Q0 1.3 GHz cryomodules operating in the CW
mode are critical technology for several major scientificprojects under construction or being planned in the world.
For example, Shanghai High Repetition Rate X-ray FEL
and Extreme Light Facility (SHINE) [1], Shenzhen
Superconducting Soft X-Ray Free Electron Laser(S3FEL) [2], and high duty cycle upgrade of the European
XFEL [3]. High Q0 will save a large part of the construction
and operational cost of the cryogenic system for theseprojects.
The successful commissioning and operation of Linac
Coherent Light Source II (LCLS-II) at SLAC first timedemonstrated high Q0 cavity in a CW superconducting RF
linac [4] with nitrogen-doping (N-doping) technology [5].
Fermilab and JLAB has achieved even ambitious
performance goals in LCLS-II-HE prototype andproduction cavities and cryomodules by improving thenitrogen doping technology [6-8].
Medium-temperature baking (mid-T bake) is a novel
high Q0 recipe discovered in 2019 [9-11] by Fermilab.
KEK simplified the implementation of the recipe by midT baking of the unassembled cavity in a normal vacuum
furnace (so called mid-T furnace baking) [12], which ismore accessible than the original in-situ mid-T bake.
___________________________________________

KEK’s systematic investigations showed that 300 C bakehas the highest Q0 [13].
Based on Fermilab and KEK’s experience on single cell
cavities, IHEP further simplified mid-T furnace bakeprocedure to only one bulk EP (without light EP) andsuccessfully applied it first time to 1.3 GHz 9-cell cavities
in October 2020 [14, 15]. Since then, fourteen mid-T 9-cellcavities have been tested with high reliability by industrial
vendors. Researches from other labs [16-19] also
confirmed the mid-T furnace bake a reproducible andstable recipe for high Q0 cavities. In June 2023, a 1.3 GHz
cryomodule with eight mid-T furnace baked 9-cell cavities
was assembled and tested at IHEP and achieved world
leading high Q0 and high gradient.
There are some distinct advantages of mid-T bakecompared to nitrogen doping [20]. Mid-T bake has been
widely applied successfully to large grain cavities [21, 22],other frequencies and shapes [23, 24] and even carried out
without furnace [25]. In particular, mid-T furnace bakehigh Q0 recipe was recently adopted for the low-beta
650 MHz 5-cell cavities for Fermilab’s PIP-II project [26].
The ongoing and future high repetition rate FEL and ERL
projects (e.g. SHINE, S3FEL, DALS, PERLE and highduty cycle upgrade of European XFEL etc.), as well as theenergy frontier circular lepton colliders (CEPC, FCC-ee)
are all considering to use mid-T furnace bake treatment for
their large number of cavities.
Therefore, demonstration of mid-T bake cavity
performance in a real cryomodule is becoming essential forthe development and practical application of this novel
high Q0 technology. In this contribution, we report theperformance of the world’s first mid-T bake cryomodule.

CRYOMODULE ASSEMBLY
AND INSTRUMENTATIONThe cryomodule structure and assembly procedure aresimilar to LCLS-II cryomodules which is modified from
Euro-XFEL design. The 12 m long cryomodule (Fig. 1)
contains eight 1.3 GHz 9-cell cavities, eight power input
couplers, eight tuners with piezos, one conduction-cooled
superconducting magnet and one BPM. Measures toreduce microphonics were adopted according to LCLS-IIexperience [27]. To avoid contamination risk, the cavity
string was kept in vacuum after leak check all through tothe horizontal test. To reduce the multipacting processing
time, the cavity string was also pumped by a turbo
molecular pump whenever possible during the cold mass

† zhaijy@ihep.ac.cn
MOAA: Monday Oral Posters

MOAA003

MC4.8 Superconducting RF

17

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HIGH Q AND HIGH GRADIENT PERFORMANCE OF
THE FIRST MEDIUM-TEMPERATURE BAKING 1.3 GHz CRYOMODULE

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOAA004

L. M. Wroe, A. Latina, J. Olivares Herrador, S. Stapnes, W. Wuensch, CERN, Geneva, Switzerland
G. Kharashvili, F. Plewinski, DAES SA, Geneva, Switzerland
Abstract
Neutron scattering is an indispensable technique in material science research for providing solutions to important
engineering challenges, including the ever-growing demand
for more efficient batteries and fuel-cells. There are, however,limitations in the access and availability to the necessary
neutron beams and this is worsening as nuclear research
reactors continue to shut down. As a result, there appears to
be market demand for an affordable, medium-flux, compact,
accelerator-driven neutron source optimised for deployment
in an industrial setting. In this paper, we present an overview
of the beam specification and the high-level design choices
for an electron linear accelerator that is optimised to drive
such a facility.

INTRODUCTION
The use of neutron beams for neutron scattering measurements finds a broad range of applications in the field of material science [1]. In particular, neutron scattering techniques
can be exploited to develop advanced battery and fuel-cellmaterials and manufacturing techniques [2–4], as well as
to measure the material stresses and strains within material
samples [5–7]. Such neutron scattering experiments andmeasurements are typically undertaken in large-scale facilities that utilise spallation sources (such as the Spallation
Neutron Source at the Oak Ridge National Laboratory in
Tennessee, US [8] and the European Spallation Source underconstruction in Lund, Sweden [9]) or nuclear research reactors (such as the High Flux Reactor at the Laue-LangevinInstitute in Grenoble, France [10]).
However, the landscape of available neutron facilities isshifting as nuclear facilities continue to close despite theever increasing demand for access to neutron beams [11].
Compact Accelerator-driven Neutron Sources (CANS) area potential answer to this problem and, despite a reduced
neutron flux at the sample compared to higher-end facilities,
they offer a series of attractive benefits. These include, forexample, the ability to develop and use advanced sample environments and instrumentation dedicated to focused topics,
the provision of high ‘access agility’, the production of lessradioactive waste, and the fact that nuclear licensing is not
required [12].
Currently, there are no commercial-off-the-shelf CANS
available to industry, universities, nor research centers.
A collaboration therefore formed between DAES SA andCERN in 2023 to further develop the so-called VULCAN (Versatile ULtra-Compact Accelerator-based Neutron
source) instrument that has been jointly developed between
2021 – 2024 by DAES SA, the Danish Technological InstiMOAA: Monday Oral Posters
MC2.5 Industrial and medical acceleratorstute, and Xnovotech. VULCAN is a compact and affordable,
non-destructive, CANS-based testing instrument that generates a cold neutron beam for neutron scattering measurements. It is purpose-built for implementation in an industrial
setting and optimised for the in-situ analysis of battery andfuel cell electrodes, as well as for the measurement of internal stresses inside thick metallic and ceramic components.
Essential to the VULCAN design is its compactness. A
conceptual visualisation of such a facility is shown in Fig. 1.
The core parts are:• Electron linac: A compact, pulsed electron-based linear accelerator that delivers 35 MeV electrons with anaverage beam power on the order of a kW to the TargetModerator-Reflector (TMR).
• Radiofrequency source: A radiofrequency powersource that drives the electron linac.
• Target-Moderator-Reflector (TMR) assembly: A compact setup optimised for the conversion of the incident
electron beam into a cold neutron beam with the desired
properties.
• Neutron guide: A neutron guide to provide time-offlight measurements.
• Hexapod and detector: A hexapod on which to position
the material sample and a detector with which to takemeasurements.
The collaboration between DAES SA and CERN has two
aims. One is to benchmark the performance of a prototype
TMR and the second is to develop a conceptual design of anelectron linear accelerator optimised for VULCAN.
This paper focuses on the high-level design choices madefor the electron linac design. We begin with a discussion of
the electron beam specification and the accelerator design
parameters that are to be optimised. The impact this has on
the high-level accelerator design is then outlined.

ELECTRON BEAM SPECIFICATION
Table 1 provides the specification on the electron beam
and accelerator design for the VULCAN facility.
The underlying reasons behind this electron beam specification are:• Beam energy and spread: The neutron yield per unitof electron beam power incident on a tungsten target
increases rapidly between 7 – 30 MeV. Bremsstrahlung
processes produce more photons with energies that havea significantly larger cross-section for exciting the giant
MOAA004
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ACCELERATOR DESIGN CHOICES FOR A COMPACT,
ELECTRON-DRIVEN, PULSED NEUTRON SOURCE

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOAA005

PERFORMANCE OF THE FERMILAB LINAC INJECTOR
Abstract
The Fermilab Linac injection line consists of a 35 keV
magnetron-type H- ion source, two-solenoid Low Energy
Beam Transport (LEBT), 201 MHz 4-rod 750 keV Radio Frequency Quadrupole (RFQ), and a Medium Energy Transport(MEBT) containing 4 quadrupoles and a bunching cavity.
The injector delivers 25 mA, 48 µs pulses to the drift-tube
Linac at a repetition rate of 15Hz. The transmission efficiency of the injector has been lower than expected sincecommissioning. Recent beam current measurements suggest that the beam is primarily lost upstream of the RFQ exit.
Numerical simulations indicate that ions passing throughthe non-linear field region of the solenoids could produce
a beam with an increased emittance resulting in up to 50%of the LEBT beam current failing to meet the RFQ acceptance. An aperture restriction was installed upstream of thefirst solenoid to remove these ions. This report describes
the results of measurements and simulations as well as the
LEBT tuning.

INTRODUCTION
The Fermi National Accelerator Laboratory (FNAL)
LINAC H- injector was upgraded from a Cockcroft–Walton 750 keV DC accelerator to a 201 MHz 4-rod 750 keVRadio Frequency Quadrupole (RFQ) injector as part ofthe 2012 Proton Improvement Plan for the FNAL complex. The H- injector line currently consists of a 35 keV
magnetron-type H- ion source, two-solenoid Low Energy
Beam Transport (LEBT), 201 MHz 4-rod 750 keV Radio Frequency Quadrupole (RFQ), and a Medium Energy Transport(MEBT) containing 4 quadrupoles and a bunching cavity [1].
The transmission efficiency from the ion source to the startof the LINAC is approximately 40% which is significantly
lower than expected. Previous studies looking at the transmission efficiency focused on the MEBT and other beamline
qualities [2]. In addition, recent data exploring the possibility that the LEBT is the main cause of the inefficiency has
been presented [3].
In this paper, we explore the use of an aperture restriction
just upstream of the first solenoid to explore the possibilityof better matching the LEBT beam to the RFQ acceptance.
This report describes the results of measurements and simulations.

NOTICING THE PHASE SPACESPIRALLING
Due to the compact nature of the H- injector the ion source,
LEBT, and RFQ have no emittance diagnostics. The first setof emittance diagnostics is at the entrance of the drift-tube
LINAC (DTL). To investigate the emittance of the beam

Figure 1: Heat maps from the ion source test bench emittanceprobesdownstream of the ion source an ion source test bench with asimilar ion source and single solenoid was used. Heat Maps
from the ion source test bench are shown in Fig. 1.
The shown phase space spiral is in both transverse planes.
This suggests a linear ”stick”-like shape of the beam in phasespaces at the ion source which is then filamented in thesolenoid field.
We suspect that this filamentation is due to the beaminteracting with the non-linear magnetic field region in thesolenoid. Assuming a ”stick”-like shape of the beam in phasespace CST Particle Studio (PS) simulations were run underfull neutralization conditions and the results showed growthand dilution of the beam emittance in the LEBT. This growthand dilution of the beam emittance in the LEBT results ina mismatch with the elliptic RFQ acceptance resulting inhigh beam loss. Further simulations indicate that an aperture
restriction upstream of the first solenoid will assist in forming
a beam emittance matched to the RFQ acceptance in sizeand shape, shown in Fig. 2.
The simulation results show that without the aperture
restriction, the beam is filamented in the X-X’ and Y-Y’planes resulting in many of the particles falling outside of the
RFQ acceptance (red ellipse). When an aperture restriction
with a diameter of 46 mm was simulated to be just upstreamof the first solenoid most of the particles fell within the RFQ
acceptance.

∗ dcjones@fnal.gov

MOAA: Monday Oral Posters
MC1.1 Beam Dynamics, beam simulations, beam transport

MOAA005
25

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D. C. Jones∗ , D. Bollinger, V. Kapin, Fermi National Accelerator Laboratory, Batavia, USA32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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STANDING WAVE DIELECTRIC DISK ACCELERATING STRUCTURE
DESIGN AND FABRICATION
S. Weatherly∗ 1 , C. Jing2 , E. Wisniewski1 , D. Doran, J. Power
Argonne National Laboratory, Lemont, IL, USA
B. Freemire, Euclid Beamlabs, USA
T. Abe, Accelerator Laboratory, High Energy Accelerator Research Organization, Japan1
also at Illinois Insitute of Technology, Chicago, USA2also at Euclid Beamlabs, Bolingbrook, USA
Abstract
A Dielectric Disk Accelerator (DDA) is a metallic accelerating structure loaded with dielectric disks to increase
coupling between cells, thus high group velocity, while still
maintaining a high shunt impedance. This is crucial forachieving high efficiency high gradient acceleration in the
short rf pulse acceleration regime. Research of these structures has produced traveling wave structures that are poweredby very short (∼ 9 ns), very high power (400 MW) RF pulses
using two beam acceleration to produce these pulses. In
testing, these structures have withstood more than 320 MWof power and produced accelerating gradients of over 100
MV/m. The next step of testing these structures will use amore conventional, klystron power source. A new standing
wave DDA structure is being fabricated for testing on the
Nextef2 test stand at KEK. Simulation results of this structure show that at 50 MW of input power, the DDA produces
a 457 MV/m gradient. It also has a large shunt impedanceof 160 MΩ/m and an r/Q of 21.6 kΩ/m. Cold testing of
this structure will be conducted late summer 2024 with highpower testing to be done in the fall.

PREVIOUS DDA PROTOTYPES
Initially, two single cell DDA structures were designed
and high power tested [4, 5]. A clamped design was selected
for new designs due to difficulties with brazing on previous
prototypes. During high power testing, the clamped single
cell DDA withstood 321 MW of input power and achieved
an accelerating gradient of 102 MV/m [6]. The test ran up
to the amount of available RF power. During the experiment
there were no optical signs of breakdown and in review of therecorded RF pulses during data processing there were also
no signs of breakdown. After testing, the single cell clamped
DDA was disassembled and visually inspected. Damage wasfound where the faces of the copper components meet whenclamped. Figure 1 shows the damage. Since the damage
was located outside the RF volume it was likely caused byuneven and insufficient clamping during assembly.

INTRODUCTION
The future path for accelerators are compact, high energy
linear machines. In order to minimize the footprint, high gradient accelerating cavities need to be developed. Dielectric
Disk Accelerators (DDA) researched here are X-band dielectric disk loaded metallic structures are a promising candidate
to be used in future accelerators. These structures have highshunt impedances and high accelerating gradients [1].
To produce high accelerating gradients, high peak input
RF power are required and to limit the risk of breakdown,
short RF pulses are used [2]. These pulses are created using
Two Beam Acceleration (TBA). A high charge drive beam
is produced and sent through a Power Extractor and Transfer Structure (PETS) [3]. This decelerates the drive bunch
and transfers the created RF power packet to the DDA that
accelerates a witness beam. The RF pulse length producedby the PETS in this research is ∼9 ns.
In this paper we will review the outcomes of previous
DDA experiments and discuss plans to test a new standing
wave DDA on a klystron test stand at KEK.
∗ sweatherly@hawk.iit.edu

MOAA00628

Figure 1: Damage seen on the copper and ceramics from thesingle cell DDA high power experiment.

Multicell DDA Structure
Following the success of the single cell clamped structure,a multicell clamped structure was designed and tested. The
fabricated and assembled structure is seen in Fig. 2.
Structure Simulation The original design of the multicell DDA involved seven dielectric disks that made up
six cells. The design emphasized maximizing the shunt
impedance of the structure while also keeping the accelerating gradient as high as possible. Simulations were donein both CST and COMSOL [7, 8]. Table 1 summarises thesimulation results for the six cell structure.
MOAA: Monday Oral Posters
MC2.6 Other electron accelerators

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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SIMULTANEOUS ACCELERATION OF PROTON
AND H-MINUS BEAMS IN RFQ
S. S. Kurennoy, Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract
The Los Alamos Neutron Science Center (LANSCE) accelerator complex delivers both protons (p) and negativehydrogen ions (H-) and provides various beam patterns
simultaneously to multiple users. The LANSCE linac front
end is still based on Cockcroft-Walton voltage generatorsthat bring proton and H- beams to 750 keV. An upgrade of
the front end to a modern, RFQ-based version is now underconsideration. The most promising upgrade option is basedon acceleration of two continuous beams, p and H-, injected
simultaneously into a single RFQ, which has never been
done before. We use an existing CST model of a proton
RFQ to model simultaneous acceleration of proton and Hbeams as a proof of principle for such an RFQ operation.

INTRODUCTION
The 800-MeV proton linac at LANSCE operates since1972 and now delivers both proton and negative hydrogenion (H-) beams of different flavors (time patterns, bunchcharges) to five user facilities simultaneously [1]. The initial beam acceleration to 750 keV is still provided by ageing Cockcroft-Walton (C-W) generators. Various options
for the front-end upgrade have been under consideration
for a long time [2]. The most promising option is based on
simultaneous acceleration of two continuous beams, p and
H-, in a single RFQ. While it is known that a proton RFQ
can also accelerate H- ions, RFQ working simultaneouslywith two beams, p and H-, has not been demonstrated.
We will use an existing CST Studio [3] model of the 4rod RFQ that was originally developed to replace the proton C-W injector at LANSCE, see in [4], while keeping theH- injection unchanged. The 201.25-MHz RFQ was designed to accelerate protons to 750 keV, fabricated by
Kress GmbH, and delivered to LANL in 2015. However,detailed 3D modeling [5] indicated difficulties of integrating such a new proton injector in the existing front end.
One important goal for the upgraded LANSCE front end
is that it should provide all beam flavors available now.
The most challenging is a special case of H- beam, which
consists of single bunches with increased bunch charge,
about 300 pC, separated by long intervals of 1.8 µs – theso-called MPEG beam. The MPEG bunches are deliveredfrom the linac at 800 MeV directly to targets, mainly fortime-of-flight experiments. Compared to regular Hbunches (called LBEG), which are injected into the Proton
Storage Ring at 800 MeV and follow at 201.25-MHz repetition rate (~5-ns period), the higher charge in MPEG
bunches is achieved by chopping about 25-30 ns of continuous H- beam at 750 keV and applying an energy tilt forvelocity bunching. MPEG bunches are not well matched to
the linac, which is tuned to beam flavors with higher average power, and a significant fraction of the MPEG beam,

up to 2/3, is lost in the drift tube linac, well before it reaches
its target, see in [6]. Generating a single high-charge bunchout of an RFQ is a challenge: it will likely be accompanied
by undesirable satellite bunches, which will need to be removed (chopped) in the following transport line, Medium
Energy Beam Transfer (MEBT).

MODELING RFQ IN CST STUDIOCST Model of RFQ
The 201.25-MHz 4-rod RFQ was designed to accelerate
proton beams from 35 keV to 750 keV. Its CST model [4]is shown in Fig. 1. Note the unusual coordinate system,
which came with the RFQ CAD model: the beam moves
from right to left, in the negative x-direction. The RFQ vacuum vessel, in light blue, is 175-cm long, 34-cm wide, and30-cm high (along the stem direction, z). The rods are supported by 24 stems, with movable tuning plates mounted
between stems. The EM fields of the operating mode were
calculated with eigensolver in CST MicroWave Studio.

Figure 1: Vacuum volume of RFQ CST model (outer box
walls not shown).
The model was used to study beam capture and acceleration with 35-keV proton macro-particle distributions generated by Parmila (L.J. Rybarcyk) and matched to the RFQ
for a few different currents. The macro-particles are evenly
distributed in phase within one RF period. The Parmila distributions were reformatted into CST Particle Studio (PS)
input – all particles are injected in a fixed plane at different
times corresponding to their RF phases. For PS simulations
we typically inject into RFQ 10 RF periods with 10K
macro-particle per period, i.e., 100K particles. Some results of PS particle-in-cell (PIC) simulations [4] with different currents are presented in Table 1, where the units foremittances are π mm∙mrad. The initial normalized r.m.s.
transverse emittance is εt = 0.2 π mm∙mrad in both transverse planes. The output normalized r.m.s. emittances aremarked as horizontal εh, vertical εv, and longitudinal εs, referencing the usual lab coordinates, because the RFQ box isrotated by 45° w.r.t. the beam axis (x here), so that the tuning plates are not vertical as in Fig. 1 but are inclined at 45°
to the floor.

MOAA007

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MC3.4 Proton linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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HIGH PULSED POWER MEASUREMENTS OF SUPERHEATING FIELDSFOR SRF MATERIALS∗
N. Verboncoeur† , A. Holic, M. Liepe, T. Oseroff, R. D. Porter‡ , J. Sears, L. Shpani
Cornell Laboratory for Accelerator based ScienceS and Education (CLASSE), Ithaca, NY, USA
Abstract
The Cornell High Pulsed Power Sample Host Cavity (CHPPSHC) is a new system designed to measure the superheating field of candidate superconducting RF (SRF) materials,
giving insight into their operational limits. This system isdesigned to reach peak magnetic fields of up to 0.5 T in only
a few microseconds, allowing us to achieve a purer magnetic field quench on the sample. We present an overview
of the CHPPSHC system and proof of principle data from aniobium sample.

INTRODUCTION
Improving the accelerating gradient, 𝐸𝑎𝑐𝑐 , of superconducting radio-frequency (SRF) cavities is a desirable goal
for the next generation of accelerators. The upper limit on
𝐸𝑎𝑐𝑐 for a given material is set by its superheating field, 𝐵𝑆𝐻 ,and the cavity geometry. Niobium cavities are the current
standard and has a 𝐵𝑆𝐻 of ∼ 200 mT corresponding to a maximum 𝐸𝑎𝑐𝑐 of ∼ 50 MV/m in an elliptical cavity [1]. The
SRF community has been investigating other materials [2,3] including Nb3 Sn, which is predicted to have a 𝐵𝑆𝐻 of ∼400 mT [4, 5]. This corresponds to an upper limit on 𝐸𝑎𝑐𝑐of ∼ 100 MV/m.
To date, there has not been satisfying experimental measurements of Nb3 Sn’s superheating field. Previous attempts
have been made, however these experiments have been
severely limited by thermal effects. The superheating field
is an extremely temperature-dependent property, so even asmall amount of heating can lower the quench field. Here,
we explore the Cornell High Pulsed Power Sample Host
Cavity (CHPPSHC), a sample host structure specifically designed to measure the limiting magnetic fields of candidate
SRF material samples [6, 7].

THE CORNELL HIGH PULSED POWER
SAMPLE HOST CAVITYThe CHPPSHC must be able to reach fields exceeding thepredicted 𝐵𝑆𝐻 of Nb3 Sn fast enough that heating does nothave a significant effect on the measurement. The CHPPSHC
utilizes a 1 MW klystron with pulse lengths on the order of
10 µs. Past experiments at Cornell were done with 1.3 GHz
elliptical cavities, but maximum fields were thermally limited due to pulse lengths of 50 - 100 µs [1]. The CHPPSHC’s
geometry is designed to charge quickly by exploiting fieldenhancement along the sharp edge of the sample. A simulation of the magnetic field in the cavity is shown in Fig. 1.
∗ Supported by U.S. Department of Energy Grant No DE-SC0008431† nmv39@cornell.edu‡ Now at SLAC, Menlo Park, California, USA

Figure 1: Simulation of peak magnetic fields along 𝑥 = 0(left) and 𝑧 = 0 (right) planes of the CHPPSHC in CST
Microwave Studio. The design exploits field enhancement
to reach significantly higher peak fields on the sample edge.
An upper bound of 1 × 105 A/m was set on the color scale
for visibility purposes. The peak field on the sample is ∼4 × 105 A/m corresponding to ∼ 500 mT.
The peak field on the sample edge is enhanced by a factorof 500 due to this effect, which allows the system to reach amaximum field of ∼ 500 mT in only ∼10 µs [6].
The simulation also calculates the quality factors of various components of the system. While superconducting,the sample accounts for less than 0.001 % of losses. Whenthe sample is normal conducting at 300 K, the losses on thesample reach ∼ 70 % of losses. The resulting sharp drop in
the system’s 𝑄0 is large enough that it will be evident in RF
power data when the sample has quenched.

PULSED RF DATA
Before investigating Nb3 Sn, baseline data for a niobium
sample is necessary to ensure that quench information canbe accurately extracted from our measurement results. A
niobium sample was prepared using the same processes
applied to a niobium cavity, receiving a bulk chemical polish,
electropolishing, and a 5 hr 800 C bake. The sample wascleaned with DI water in a class 100 cleanroom before being
assembled into the copper host structure.
The host cavity is tested in helium over a temperature
range from 2 K to 9 K and driven by a 1 MW klystron. Before taking pulsed data, a system calibration is done in continuous wave (CW) operation to determine the loaded quality
factor, 𝑄𝐿 , the coupling, 𝛽, and field calibration. In Fig. 2,
an example pulsed operation data point is shown. 𝐵𝑝𝑘 is
calculated from the RF data using the results of the CW
calibration and the CST simulation.
Figure 2 shows a pulse that exhibits “overfilling” behavior
where the cavity continues to fill despite the sample quenching. This makes it more difficult to accurately identify thequench field as the underlying mechanisms become more
complex.

MOAA008

MOAA: Monday Oral Posters

36

MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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LOW ENERGY MULTI-BEAM DYNAMICS INNOVEL LANSCE FRONT END
Y. K. Batygin, Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Abstract
The proposed novel 100 MeV injector for the LANSCE
Accelerator Facility [1] is designed to replace the existing
750-keV Cockcroft-Walton-columns-based injector. The
new Front End includes two independent low-energy transports for H+ and H- beams merging at the entrance of a single RFQ, with the subsequent acceleration of particles in
the new Drift Tube Linac. The challenge of the design isassociated with the necessity of simultaneous accelerationof protons and H- ions with different beam currents, beam
charges per bunch, beam emittances, and space charge depression, in a single RFQ and DTL, while injection beamenergy is reduced from 750 keV to 100 keV. Accelerationof various beams in a single RFQ provides less flexibility
for optimal adjustment of acceleration and focusing parameters concerning the existing LANSCE setup. The paper
discusses multi-beam dynamics in the proposed injector.

FORMATION ON MULTI-BEAM
STRUCTURE IN LEBTA unique feature of the LANSCE accelerator facility is
its simultaneous acceleration and delivery of various
beams to multiple targets [2]. Protons with energy of 100MeV are delivered to the Isotope Production Facility (IPF),
while the 800-MeV H- beam is distributed to four experimental areas: the Lujan Neutron Scattering Center
equipped with the Proton Storage Ring (PSR), Weapons
Neutron Research Facility (WNR), Proton Radiography(pRad), and Ultra-Cold Neutron facility (UCN). To reduce
long-term operational risks and to realize future beam performance goals in support of the laboratory missions, wedevelop a novel Front End including a high-brightness Radio-Frequency Quadrupole (RFQ) based injector [1, 3, 4],
see Fig. 1. The low-energy part of the novel injector includes two independent transports for the proton and H-

beams with multiple flavors of the beams merging at theentrance of a single RFQ.
Details of the time structure of accelerated beams are
given in Ref. [1]. The multi-beam structure is achieved in
Low Energy Beam Transport through a combination of
chopper and RF bunchers. Among all the beams, the Hbeam delivered to the WNR facility exits only as a combination of single bunches, separated by long time intervals,
while other beams are trains of bunches with various pulse
lengths.
Figure 2 illustrates only two modes of chopper operation: long pulse mode for the beam injected into the Proton
Storage Ring, and short pulse mode used for the preparation of single bunches for WNR facility. The chopper isnormally energized so that no beam gets through. An electrical pulse of length 25 ns and 290 ns for short and longbunch modes, respectively, travels along the chopper allowing the un-chopped part of the beam pulse to passthrough, see Fig. 3. The minimum width of the chopper
pulse is determined by the chopper’s rise time, which isabout 10 ns. The long bunch pulses feed the chopper at therate of 2.8 MHz, which corresponds to one pulse every 358
ns, which is the revolution time for the Proton Storage
Ring. Following the chopper, the leading and trailing edgesof the beam are bent vertically, which affects the beamemittance.
Figure 4 illustrates the formation of a single WNR bunchusing the short pulse mode of the chopper. The chopper
cuts ~ 25 ns beam followed by beam energy modulation in
the 16.77 MHz Low-Frequency Buncher. In the downstream drift space, the energy modulation is transformed
into beam density compression resulting in a single WNRbunch with a substantially larger charge per bunch than thatobtained by 201.25 MHz acceleration of other beams. The
WNR bunch is then accommodated in the 201.25 MHz RF

Figure 1: Layout of the proposed 100 MeV LANCE Front End Accelerator Facility [1].
___________________________________________

batygin@lanl.gov

MOAA01040

MOAA: Monday Oral Posters
MC3.2 Ion linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA

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ISSN: 2226-0366

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BEAM OPTICS DESIGN OF A PROTOTYPE 20 KW
CONDUCTION-COOLED SRF ACCELERATOR FOR
MEDICAL STERILIZATION ∗A. Saini† , C. Edwards, I. Gonin, Y. Ji, T. Kroc, N. Solyak, V. Yakovlev, Fermilab, Batavia, IL, USA
Abstract
Superconducting technology has significantly advanced
the capabilities of particle accelerators, facilitating higher
beam-power operations for fundamental research at a comparatively lower cost. However, the conventional implementation of superconducting technology introduces complexities in the form of cryogenic plants, cryogenic distribution
systems and substantial construction and operational cost. In
response to these challenges, recent research efforts at Fermilab have been dedicated to the development of a cryogen-free,conduction-cooled Nb3Sn-based superconducting technology. This paper outlines the beam optics design of a 20-kW
conduction-cooled compact superconducting accelerator for
medical sterilization. The paper reviews both the physics
and practical constraints associated with high beam-power
operation within the context of industrial applications. The
focus is on providing insights into the potential of this innovative technology to overcome existing challenges and pave
the way for more accessible and efficient industrial particle
accelerators.

wastewater, sludge, removing pollutants from stack gas-es,
medical wastes and many more [1].

20 KW COMPACT SRF ACCELERATOR
A team of researchers and engineers at Fermilab has beenworking to develop a prototype cryogen-free, conduction
cooled [2] Nb3Sn based, 20 kW, Continuous Wave (CW),
electron SRF accelerator. Note that, Nb3Sn coated cavities
significantly reduce cryogenic losses and allow for operation at higher temperature (i.e., 4. K vs 2.0 K). This, inturn, enables the replacement of complex cryogen-based
cooling systems with commercially available cryocoolers,
resulting in a smaller infrastructure footprint, highly reliable
and simplified superconducting operation with minimal expert’s involvement. Thus, this prototype SRF accelerator
represents a significant milestone in establishing the feasibility of beam accelerating using conduction cooled Nb3Sn
SRF technology. A successful demonstration will set thestage for building a full-scale, high power SRF accelerator
facility, aimed at providing megacurie-level capabilities as areplacement for Cobalt-60 (Co-60) irradiation facilities.

BACKGROUND
Superconducting Radio Frequency (SRF) accelerating
structures provide higher accelerating fields with minimal
power dissipation, making them highly energy-efficient andcapable of delivering significant energy-gains. These advantages make SRF technology the preferred choice for particle
acceleration in large research facilities. Despite its potential
to extend the particle accelerators into emerging applications and enhance the efficiency of existing processes, SRF
technology has not yet been fully adopted in the commercial
sector. This is mainly due several practical challenges associated with conventional SRF accelerators, including (a) thesignificant initial capital investment required to establish an
SRF facility, (b) comparatively a larger footprint of the overall infrastructure, (c) complexity of routine operation andmaintenance associated with cumbersome systems such as
cryo-plant and cryogenic distribution and (d) need for highly
skilled personnel to manage and maintain the facility. To
overcome these challenges, recent research and development
efforts at Fermilab have been focused on developing enabling
technologies to simplify and reduce the construction andoperational cost of SRF particle accelerators for a varietyof energy and environmental applications including but notlimited to medical sterilization, treatment of potable and∗ Work supported by Fermi Research Alliance, LLC under contract no.

DE-AC02-07CH11359 with the DOE, USA† asaini@fnal.gov

MOAA01144

Figure 1: Render view of 20 kW prototype accelerator.
The accelerator is designed to deliver 12.5 mA electron
beam current at 1.6 MeV in CW regime. Figure 1 shows
rendered view of 20 kW prototype accelerator beamline.
Its critical components can be organized into three major
sections: (a) Integrated electron gun, (b) SRF section and(c) Beam delivery system.
MOAA: Monday Oral Posters
MC2.5 Industrial and medical accelerators

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOAA012

F. H. O’Shea† , J. D. Cruz, A. Edelen, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
J. Edelen, M. Henderson, RadiaSoft, LLC, Boulder, CO, USA
Abstract
RadiaSoft is developing machine learning methods to improve the operation and control of industrial accelerators.
Because industrial systems typically suffer from a lack of
instrumentation and a noisier environment, advancements
in control methods are critical for optimizing their performance. In particular, our recent work has focused on thedevelopment of pulse-to-pulse feedback algorithms for use
in dose optimization for FLASH radiotherapy. The PHASER(pluridirectional high-energy agile scanning electronic radiotherapy) system is of particular interest due to the need tosynchronize 16 different accelerators all with their own noisecharacteristics. This presentation will provide an overview of
the challenges associated with RF tuning for a PHASER-likesystem, a description of the model used to evaluate different
control schema, and our initial results using conventional
methods and machine learning methods.

FLASH RADIATION THERAPY
There is empirical evidence for increased tumor control
probability and decreased normal tissue complication probability when ultrahigh dose rates are used to treat cancerous
tumors, so-called FLASH radiation therapy [1]. An exampleof the FLASH effect is given in Fig. 1. Current systems used
for radiation therapy typically deliver dose at the ≲1 Gy/min
rate, while evidence for the FLASH effect typically occurs at≳40 Gy/s. In either case, the expected dose is approximately
10 Gy, meaning that, for FLASH, the total treatment timeis less than 250 ms, and usually much less. As such, newaccelerator technology is required to deploy FLASH in theclinic [2, 3]. One such proposed system is the PHASER(pluridirectional high-energy agile scanning electronic radiotherapy) [4].
A schematic of the PHASER system is shown in Fig. 2.
The PHASER uses 16 beams (as opposed to a gantry) toallow fast tracking of targets that are monitored via an integrated computed tomography (CT) scanner. The RF macropulse length will be 300 ns long. The second generation
PHASER, which will treat patients directly with electrons,
also plans to use pulse shaping of the photo-cathode laser
to allow for intensity-modulated radiation therapy withouta slow multi-leaf collimator. These new features require a
new kind of fast control (well sub-second) that is able touse the CT images to help determine where to apply theplanned dose [5]. Artificial intelligence is a candidate suiteof solutions for everything from tracking tumor motion tocontrolling the dose profile.
∗ This work is supported by the DOE Office of Science Office of Accelerator

Research Development and Production award number DE-SC0023641.

† foshea@slac.stanford.edu

MOAA: Monday Oral Posters
MC2.5 Industrial and medical accelerators

Figure 1: Survival fraction of human prostate cells after a
FLASH treatment from protons (top) and a normal treatment
from x-rays (bottom). Normal cells are denoted RWPE1 andcancerous cells are denoted PC3. Image adapted from [6]under the Creative Commons Attributions License [7].
Herein, we present some initial results on controllingsome relevant RF system properties of the PHASER. After constructing an accessible model of power combinationfrom multiple klystrons, we will show that the system admits solutions using both reinforcement learning and linear
regression.

Figure 2: Conceptual design of the PHASER system showing the 16 linacs directed towards a patient phantom. The
white ring that shares an isocenter with the accelerator beams
is a computed tomography (CT) scanner. Image courtesy ofGreg Stewart/SLAC National Accelerator Laboratory.
MOAA01247

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AUTOMATION OF RF TUNING FOR MEDICAL ACCELERATORS∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB001

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ALBA INJECTOR RELIABILITY IMPROVEMENTWITH AN 80 MeV LINAC BEAM
R. Muñoz Horta, D. Lanaia, F. Pérez, ALBA Synchrotron, Cerdanyola del Vallès, Spain
Abstract
The ALBA injector consists of a 110 MeV Linac, a
Linac-to-Booster Transfer Line (LTB) and a full energy
Booster that further accelerates the electrons up to 3 GeV.
The Linac consists of two pre-bunchers (PB1 at 500 MHz
and PB2 at 3 GHz) a buncher and two accelerating structures (AS1 and AS2). The whole system is powered by twopulsed 37 MW klystrons at 3 GHz. To overcome an eventual klystron failure the injector has been adapted to keep
operative at lower Linac beam energy. In 2014 the injection into the Booster was optimized for a Linac beam of
67 MeV, which is the energy achieved using only one klystron. However, the procedure of switching the injector
from a Linac beam of 110 MeV to a 67 MeV one is notstraighforward and it requires to be periodically updated.
After a recent waveguide modification the RF-power sent
to the first accelerating structure is equally distributed between both accelerating structures. As a result, a Linac
beam of 80 MeV is achieved using only one klystron. The
injection into the Booster in this mode is expected to beefficient and stable enough to be set as the nominal Linac
operation mode. Furthermore, setting the nominal Linac
beam energy at 80 MeV the injector operation will be assured by the hot-spare klystron in case of klystron failure

INJECTOR VERSALITY
An overview of the whole ALBA injector [1] is shownin Fig. 1. The Linac is placed in a separate bunker whereas
the Booster is placed in the same tunnel than the Storage
Ring. The Booster lattice has a four-fold symmetry with acircumference of 249.6 m. On-axis injection from the
Linac to the Booster is achieved by using a single septum
and a single kicker.

Figure 1: Schematics of the ALBA Synchrotron. All the
injector elements are marked in red.

Since 2012 the nominal operation mode of the Linac is a108.5 MeV beam consisting of 40 bunches with a total
charge of 0.2 nC and 0.05 nC/bunch. In this mode klystron1 (KA1) feeds the 3 GHz bunching cavities (PB2 and BU)
and the first Accelerating Section (AS1) whereas klystron2 (KA2) feeds exclusively AS2.
Injector operation versatility was first improved in 2014
by installing an S-band switching system in the Linac
waveguide that allows using KA2 instead of KA1 in caseof KA1 failure [2]. The schematics of the Linac waveguidewith the implemented S-band switching system is shownin Fig. 2.

Figure 2: Schematic of the Linac RF-cavities and its waveguide system, including the S-band switching system installed in 2014.
Powering only the bunching part and AS1 with KA1 theLinac delivers a 67 MeV whereas using KA2 the beamachieved is limited to 60 MeV due to arcs in the waveguide.
The power distribution of the nominal operation mode at
108.5 MeV and of the two low energy modes using only
one klystron are shown in Table 1.
Table 1: RF-Power Distribution of the Current Operation
Modes of the ALBA Linac
Mode

Energy
[MW]

KA1
[MW]

KA2
[MW]

BU
[MW]

AS1
[MW]

AS2
[MW]

Nominal

108.5

30

13

5.8

19

11.5

KA1 only

67

26

5.2

17

KA2 only

60

22

4.5

16.2

The whole injector (LTB, pulsed elements and Booster)
was then adapted to make possible the injection (and further acceleration to 3GeV) of the low energy beam delivered by the Linac using only one klystron. Beam capture
into the Booster at low beam energies was achieved despitedifficulties due to non-linear effects in the Booster magnetic fields [3]. The magnetic field distortions are producedby eddy currents induced at the bending magnet vacuum
chambers. These effects become more significant at lower

MOPB001

MOPB: Monday Poster Session

50

MC2.7 Synchrotron light sources

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB003

A. Ravichandran†, B. Mustapha, Argonne National Laboratory, Lemont, IL, USA
Abstract
Successful implementation of AI/ML models for online
tuning of accelerators highlights the need for accurate simulation of beamline elements. Deployment of such models
requires the inclusion of realistic element misalignments
during the simulation process. This paper presents an original method to determine misalignments across entire
beamlines and apply them to the previously developed
TRACK simulation model. Validation has been performed
using experiment data in this study for a newly commissioned section of ATLAS called the Argonne Material Irradiation Station (AMIS) and an existing straight latticeknown as the PII-BOOSTER. A preliminary study for the
AMIS line shows the average difference in beam transmission between experiment and simulation for 28 tuningcases has dropped from ~46% without steering to ~16%
after applying steering and further down to ~6% after accounting for 4 quadrupole misalignments in the simulation.
Given these values and the well-established accuracy of the
TRACK model, major deviations in element positions
could be narrowed down enabling engineers to perform thenecessary alignment corrections, and possibly eliminating
the need for some steering elements. Predictability of the
TRACK code has been shown to significantly improve after applying realistic alignment and steering corrections.

INTRODUCTION
Simulation of beamline elements is vital in the design of
new lattices and making modifications to existing structures. However, even the most advanced models fail to accurately replicate experimentally measured data due tomisalignment in lattice elements. Moreover, codes such as
Methodical Accelerator Design software (MAD-X) that
employ transfer matrices to simulate FODO lattices currently do not have the capability to account for such miscellaneous errors. The TRACK beam dynamics code developed at Argonne National Lab employs the particle
tracking approach in which equations of motion are solved
using Runge-Kutta based solvers. This approach is moreamenable to account for misalignments. A recent update to
the TRACK code has incorporated a separate misalignment
function that can be setup along with the other elements
when building up the lattice for simulation. Both rotational
and translational misalignments in three dimensions can be
accounted for via this function. Although currently used
only for quadrupole misalignments, the tool supports simulating misalignments for most other types of elements.
Misalignment in accelerator components may lead toemittance growth, beam losses and breakup of the beam.

Although misalignment in beam position monitors do not
deflect the beam, they significantly compromise the effectiveness of any optimization that is implemented to tune
the device. Ganesh Tiwari et al., [1] report on the effects oftransverse spatial misalignment on the performance andstability of X-ray free electron oscillators. Given the current trend in development of smaller accelerators, Silva etal., [2] present a statistical method to determine the tolerances in misalignment of a set of lenses for such small machines. As part of this method, particle losses as a functionof alignment accuracy of optical elements in a lattice isfound. Marco Venturini et al., [3] present a method tomodel particle ray tracing through misaligned elements bysandwiching the transfer-map for aligned elements between two transformations, one applied at the entrance andone at the exit. Beam-based alignment methods account for
misalignments without evaluating the values associatedwith each element of a lattice. The work presented in thisresearch in contrast, offers an attractive alternative approach using the TRACK code to determine actual valuesof misalignment associated with quadrupoles. These values
could then be used both in simulations to correct for error
in predictions and during the design processes of new lattices by making suitable modifications. Two methods areproposed to this extent.

TRANSMISSION BASEDMISALIGNMENTThis section provides a procedure to determine misalignment in quad elements along a single straight lattice solely
employing experimentally measured values of transmission across the lattice. A straight lattice section known as
the PII-BOOSTER line at the ATLAS LINAC was used tothis extent (Fig. 1).

___________________________________________* Work supported by the U.S. Department of Energy, Office of Science-Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Figure 1: PII-BOOSTER lattice.

† aravichandran@anl.gov
MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

MOPB003
53

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EXTRACTING CRITICAL BEAMLINE ELEMENT MISALIGNMENTS
FROM DATA USING A BEAM SIMULATION MODEL*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB004

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APPLICATION OF SURVEY AND ALIGNMENT TECHNIQUESFOR BEAMLINE INSTALLATION*
A. F. Grabenhofer†, Argonne National Laboratory, Lemont, IL, U.S.A.
Abstract
The installation and alignment of new beamlines andbeamline components is necessary at any accelerator facility. The equipment and methods used to perform these precision driven tasks must be accurate, reliable, and above
all, easily repeatable. Using coordinate measuring machines (CMM), laser trackers, combined with Spatial Analyzer (SA), Autodesk Inventor, and other custom tools, it ispossible to rapidly and accurately take an idea from model
to reality, as shown through the construction of the ATLAS
Multi-User beamline.

Monuments
Monuments are fixed reference points in the environment, usually target holders for laser tracker targets orprobe tips, but can be anything as long as they are globally
fixed (they cannot be moved without great effort). Monuments serve two purposes: to correlate the CAD model andthe environment and to allow the precision measuring devices to locate themselves in the environment. In the casewhere no monuments exist, monuments may be chosen orplaced after some reference data is taken.

OVERVIEWDIRECT MEASUREMENTS

Accelerator beamline construction, with some variation
in tools, follows a relatively simple process: design and installation. I will focus on the installation and alignment of
the beamline devices. This process starts with design andsite preparation, direct measurements, fiducialization ofparts, and finally installation and alignment.

Direct measurements are just that: data taken directly withthe measurement device. In the case for the AMUU, I use
both laser tracker (Leica AT960) and portable CMM (Hexagon Absolute ARM 85 shown in Fig. 1) to perform all themeasuring both the environment and installed devices.

DESIGN AND SITE PREPARATION
Design preparation is simply the analysis of the final design, allowing the design to go from a CAD model into thereal-world dimensions and values. Often this is done byusing the dimensions already known: length, width, height,
diameter, etc. With this information, I start looking at theenvironment where the construction will take place. Correlation of the design and environment is important, asmany devices may require permanent fixtures. The 80 degree bending magnets for the ATLAS Multi-User Upgrade(AMUU) are 6600 lb magnets that require steel stands anchored into concrete. Placement of these stands is vital as
once they are installed, they cannot be repositioned without
great effort (new concrete, etc.).
In addition to the stands, the magnets themselves define
the path for the new beamline. While they have some adjustment with the stands, they need to be as close as possible to perfect prior to the final alignment (anything morethan a 1-inch offset could result in a failed installation).
From the CAD model of the installation, we know where
the bending magnets should be placed relative to existing
beamline devices (also important for achromatic1 beam delivery). For correlating the CAD model to the environment, we need monuments.
___________________________________________*Work supported by U.S. Department of Energy Office of Science, Office of Nuclear Physics, under contract number DE-AC02-06CH11357
and used resources of ANL's ATLAS Facility, which is DOE Office of
Science User Facility†
agrabenhofer@anl.gov
1
Achromatic beam delivery means that the beam has the same phasespace profile entering and exiting a section of beamline
MOPB004
56

Figure 1: Leica AT960 (left) and Hexagon Absolute ARM
85 (right).
For the AMUU, I started by taking direct measurementsof the currently installed beamline which the new beamline
was to be added to. This served as my initial reference data
and allowed me to add monuments (small magnetic holders) to the existing structure to serve as my device locating
points as well as reference points for any future changes. I
was able to correlate the data between the existing beamline and the CAD model (which included the existing section of beamline as well as the new sections) in SA (Fig. 2).
MOPB: Monday Poster Session
MC4.5 Other technology

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB007

P. Owen†, T. Powers, Jefferson Lab, Newport News, USA
Abstract
Superconducting RF (SRF) structures are susceptible tofrequency detuning from external vibrations and modal
mechanical resonances in the structure. These small disturbances, known as microphonics, require additional RF
power in CW accelerating structures since the frequency isconstantly shifting. In the Jefferson Lab CEBAF accelerator, time and frequency data of this frequency shift havebeen recorded for many years, allowing a retrospective
analysis of different microphonics-mitigation techniques.
Some of these techniques are specific to the design of each
CEBAF cryomodule, for example implementing BNNT
damping material on the cavity string. Other techniques areuniversal such as affixing vacuum lines and reinforcing
waveguide structures.

MICROPHONICS
In a resonant structure such as an SRF cavity, the resonant frequency is a function of the structure’s geometry.
Any vibration will deform the geometry slightly and thecorresponding resonant frequency.
Superconducting cavities have a very narrow bandwidth(10s–100s of Hz). For on crest beam, the required RF
power is given by the following:𝑃𝑃 =(𝛽𝛽 + 1)𝐿𝐿𝛿𝛿𝛿𝛿 2
2
��𝐸𝐸 + 𝐼𝐼0 𝑄𝑄𝐿𝐿 (𝑟𝑟⁄𝑄𝑄 )� + �2𝑄𝑄𝐿𝐿
𝐸𝐸� � , (1)4𝛽𝛽𝑄𝑄𝐿𝐿 (𝑟𝑟⁄𝑄𝑄)
𝑓𝑓0

where 𝛽𝛽 ≅ 𝑄𝑄0 ⁄𝑄𝑄1 , E is the accelerating gradient in V/m,𝐼𝐼𝑜𝑜 is the beam current in amperes, 𝑓𝑓0 is the frequency of the
RF drive, (𝑟𝑟⁄𝑄𝑄 ) is the normalized shunt impedance of thecavity in Ω/m, 𝐿𝐿 is electrical length of the cavity in meters,and 𝛿𝛿𝛿𝛿 is the difference between the frequency of the RF
source and that of the cavity.
Every structure or cryomodule design will have different
natural frequencies for mechanical resonance. It is up to thedesigner of a cryomodule to predict these frequencies andensure they do not align with frequencies commonly foundin the accelerator tunnel environment which would excite
the natural resonance. The CEBAF C100 cryomodule resonances have been well studied through simulation andmodal testing at various stages of assembly [1]. The cavity
string is suspended in a space frame with nitronic rods. It
is further constrained by the waveguides, tuners, and cryogenic beam pipe transitions to the insulating vacuum vessel.
There are four primary resonant modes which affect thecavity geometry. The lowest frequency mode, occurring at___________________________________________* Work supported by the U.S. Department of Energy, Office of Science,
Office of Nuclear Physics under contract DE-AC05-06OR23177.
†
powen@jlab.org
MOPB: Monday Poster Session
MC4.2 Cryomodules and cryogenics

10 Hz, occurs as the entire cavity string moves along thebeam line direction The next significant mode, 20 Hz, occurs as one half of the cavity string moves 180° out ofphase with the other half. The third significant mode occurs
at 40 Hz and are the resonances of individual cavity, which
can be transferred to neighboring cavities as there are no
bellows in between cavities. The fourth mode is a 90 Hz
mode where the tuner stack tends to oscillate in a horizontal plane.
All these frequencies are approximate and vary per cavity and per cryomodule. Furthermore, these modes can interact with each other. For example, when a tuner motor
operates it will induce a 90 Hz oscillation in the corresponding cavity. If this happens to be in phase with a 10 Hz
string mode, the 10 Hz mode can be amplified and cause acavity trip. For some cavities this is the typical form of a
microphonics trip [2].
When peak microphonics exceed the available RF powerand control system phase margin, the cavity will go into a
fault state which interrupts beam operations. As microphonics in C100 cryomodules have adversely affectedbeamtime at CEBAF, much effort has been made to reduce
the sources or impact of microphonic vibration. There aremany types of cryomodule in the accelerator, however the
C100 cryomodule design is particularly susceptible to vibration [1].

SOURCES AND MITIGATIONS
Mechanical resonances of the structures can be excitedby both transient and continuously occurring sources andresonate within the cryomodule structure with minimal
damping. Additionally, one can get driven vibrations thatare excited by external sources. Some of the more universal
sources are discussed below, along with current mitigation
techniques used in CEBAF.

Waveguides
Waveguides carry RF power from klystrons or amplifiers in above-ground service building to a cavity in the underground accelerator tunnel (Fig. 1). These are long rigid
structures, approximately 25 feet in length. Transfer function measurements were conducted on the waveguide withan instrumented hammer and accelerometer to excite thestructure and measure the modal transfer function.
The tests showed significant resonances at 10, 24, 44,
and 78 Hz. A series of Unistrut braces were installed tostiffen the waveguides combined with Sorbothane® pads
to dampen the motion [3]. The reinforcing structures successfully damped the resonant modes of waveguides as isshown in Fig. 2. This method of dampening is relatively
easy to test for and implement.
MOPB007
59

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AN OVERVIEW OF MICROPHONICS IN CEBAF AND
CURRENT MODERATION TECHNIQUES*

J. Dooling† , W. Berg, A. Lumpkin, P. Piot, Y. Sun, K. P. Wootton, A. Zholents
Argonne National Laboratory, Lemont, IL, USA
Abstract

Advantages

We discuss the need for a new photo-cathode (PC) gun
drive laser for the Advanced Photon Source Upgrade (APSU) linac. As context, the characteristics associated with thecurrent system are presented. The proposed new drive laser
is based on a Ytterbium (Yb) gain medium and is capableof multi-kHz operation (although presently only 30 Hz isneeded for injection into the particle accumulator ring in
support of APS-U). The pulse charge specification is 1 nC.

INTRODUCTION
In a photoinjector system the main components are the rf
gun, the photocathode, and the drive laser matched in wavelength and pulse energy to generate sufficient charge for theapplication. With our present Cu photocathode quantum efficiency, the UV harmonic near 260 nm is needed to obtain the
micropulse-charge target in support of the Advanced Photon
Source Upgrade (APS-U) operations and linac experiments.
A Ytterbium-based photocathode gun drive laser is proposed
for the linac to replace the existing antiquated Nd:Glass laser.
The proposed laser will readily operate at 30 Hz providing
0.3 mJ of 257-nm UV radiation per pulse yielding 1 nC from
our Cu cathode, s-band gun in support of user operations.
In addition, the laser allows generation of lower-charge, lowemittance electron beams for high-brightness experimentsin the APS Linac Extension Area. An advantage of updating
the PC Gun drive-laser is that the gun beamline includes
a 3-meter-long s-band accelerating structure; this provides
an additional 35-40 MeV of energy at the linac output overwhat is presently available from either of the two thermioniccathode guns. Higher linac output energy is essential forhigh-charge operation of the new storage-ring. We outline
the laser physics requirements for our LCLS-I-style PC gun
and summarize the expected beam performance.

CASE FOR A NEW PC GUN DRIVE LASER
Our present Nd:Glass CPA drive laser does not have sufficient energy to generate the 1-nC micropulse charge at
30 Hz specified for operations support, and it is no longer
supported by the vendor. Our focus is on the Pharos laser
systems built by Light Conversion. Light Conversion specializes in Ytterbium (Yb)-based femtosecond laser sources
for industrial, medical, and scientific applications.
∗ Work supported by the U.S. D.O.E., Office of Science, Office of Basic

Energy Sciences, under contract number DE-AC02- 06CH11357.

† dooling@anl.gov

MOPB0080• Modern laser system with controls and diagnostics (turnkey)–less effort required to maintain the laser• Yb-based fiber lasers are competitively priced, andoffer better stability and reliability than conventional
Titanium-Sapphire systems.
• SLAC National Laboratory is moving to these systems
and away from Ti:Sapphire-based lasers• Backup source for operations• Low-emittance beams for high-brightness experiments (e.g., Advance acceleration concepts, Compton
backscattering, Microbunching)• Improved timing stabilization, reduced jitter• Calibration of fast diagnostics (e.g., impulse response
function for fast detector deconvolution)• Yb-based system has a broader gain-bandwidth allowing for shorter pulses than the present Nd-based system.
Yb mode-locked pulses can be as short as 50 fs.
• The Yb-doped medium lases between 1030 and
1070 nm with an upper excited state in the 970-980 nm
range. This allows for efficient diode laser pumping.
Nd also has this advantage, but the difference between
the Nd upper excited state, 808 nm and the lasing level,1053 nm, is greater leading to a larger quantum defectwhich appears as lost as heat in the laser medium.
• Operating with a fundamental wavelength at 1 micron
is inherently safer then 700-800 nm (Ti:Sapph).

Disadvantages• Quenching where the excited atoms emit spontaneously
rather than via cavity-defined stimulated emission.

EXISTING ND:GLASS CPA SYSTEM
Oscillator and Amplifier
The existing PC gun laser is based on a chirped-pulsed
amplifier (CPA) design employing an oscillator seed followed by a regenerative amplifier (regen), utilizing Nd:Glassas the gain medium [1, 2]. In 2010, the amplifier flashlamps were replaced with high-efficiency, high-power 805nm laser diodes, significantly reducing thermal loading on
the phosphate-glass laser rods. The 1.8-m folded-cavity regen is shown schematically in Fig. 1. This system as well as
the oscillator (not shown) will be replaced.
Though diode pumping greatly reduced thermal effects inthe 3-mm diam. Nd:Glass laser rods, operation at a sustained
30-Hz rate has been problematic. Figure 2 shows the effecton energy per pulse and spot size as the laser rep rate isvaried from 2 to 30 Hz. The APS-U linac operates in a
30-Hz burst mode and injects into the particle accumulator
MOPB: Monday Poster Session
MC1.2 Electron and ion sources, guns, photo injectors, charge breeders

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PHOTOCATHODE DRIVE LASER UPGRADE FOR THE ADVANCED
PHOTON SOURCE LINAC∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB016

G. Moreno† , D. Gavela, M. Lopez, P. Calvo,
A. Rodríguez, J. Etxebarria, C. Oliver, J. M. Pérez, CIEMAT, Madrid, Spain
J. Giner, ICMUV, Paterna, Spain
J. M. Carmona, M. Alvarado, X. Arrillaga, AVS, Elgoibar, Spain
U. Etxebeste, Egile Mechanics S.L., Gipuzkoa, Spain
A. Lombardi, A. Grudiev, CERN, Geneva, Switzerland
Abstract
This work is part of the development study of a linac
injector for hadron therapy with carbon ion beams. The
initial cavities of the future injector consist of two 750 MHz
Radio Frequency Quadrupoles (RFQ), which are based on
the compact CERN High-Frequency RFQ. These RFQs aredesigned to accelerate the ions from 15 KeV/u to 5 MeV/u.
Each RFQ, with a length of more of 2 meters, comprises
four individual modules and 32 tuners, 8 per module.
Certain design choices, manufacturing imperfections, andmisalignments lead to local variations in the frequency andfield distribution within the RFQs. The tuning procedurecorrects these perturbations in the TE210 operating modeusing a bead pull system and movable tuners.
The aim of this article is to determine the maximum fieldcorrection achieved through this tuning without affecting thebeam dynamics. For this purpose, a set of electromagnetic
deviations that introduces significant dipole components tothe cavity is simulated, using CST Studio. Using the tuningalgorithm, this EM deviation is corrected in a realistic way.

INTRODUCTIONCIEMAT, in the framework of the IKERTU project, leadsa national collaboration that includes both industrial companies and research centers. This project aims to develop
an optimized linear carbon ion injector, named LINAC6+,
for use in hadron therapy. Carbon ions have proven to be
more precise and effective than conventional radiotherapy
in treating certain types of cancer. However, the technologyof the accelerators required for this therapy needs further development to optimize their performance and efficiency [1].
For this reason, the project focuses on the technological advancement of LINAC6+, which could be integrated into theinitial phase of a synchrotron or a complete linac.
The study aims at enhancing efficiency and compactness
while mantaining a careful beam dynamics design. The
baseline linac layout involves an EBIS ion source, 750 MHz
RFQ and IH-DTL cavities, capable of providing C6+ ion
beams up to 10 MeV/u with currents of 190 µA and pulsesof 5-10 µs at repetition rates of 200-400 Hz.

Two RFQs have been designed at CERN for this purpose [2], adapted from the compact design of the proton
HF-RFQ [3], with an special trapezoidal vane modulationthat enhances acceleration efficiency. Table 1 lists the main
specifications of the first RFQ.
Table 1: Main Specifications of the First RFQ [4]Parameter

Value

Frequency
Length 𝐿
Intervane Voltage 𝑉0
Surface Power Loss 𝑃0
External Quality Factor 𝑄𝑒𝑥𝑡
Coupling Strength
Number of Tuners
Number of Couplers
Number of Vacuum Ports

749.48 MHz
235 cm
50 kV
244 kW
5000
1.35
32
4
12

Certain manufacturing imperfections, and misalignments,
both in the areas of the apertures and in the more external
regions, lead to variations in the capacitance and inductanceof the cavity. These changes will result in a shift in the cutoff
frequency 𝑓𝑐𝑜 , and consequently, in the voltage distribution
as follows [4]:𝛿𝑉𝐿 2 𝛿𝑓𝑐𝑜
𝜋2 𝐿 2 𝛿𝐶 𝛿𝐿= 𝜋2 ( )
=−
( ) (
+
)
𝑉
𝜆
𝑓𝑐𝑜
2 𝜆
𝐶
𝐿

(1)

This variation in voltage will also be reflected in the magnetic fields of each quadrant. This can be quantified by thefollowing three components: a quadrupole component 𝑄
and two dipole components 𝐷𝑆 and 𝐷𝑇 , defined as:
𝑄=

𝐵1 − 𝐵2 + 𝐵3 − 𝐵4
𝐵 − 𝐵3𝐵 − 𝐵4, 𝐷𝑆 = 1, 𝐷𝑇 = 2422† gabriela.moreno@ciemat.es

The appropriate sign must be assigned to account for
the alternating orientation of the TE210 quadrupole mode
field in the four quadrants 𝐵𝑖 . In the absence of any errors,
the dipole components 𝐷𝑆 and 𝐷𝑇 would be zero, and thequadrupole component 𝑄 would correspond to the correctmagnetic field in each quadrant.
In the case of misalignment, the tuning process involves
correcting the mixing of resonant dipole fields by adjusting

MOPB: Monday Poster Session

MOPB016∗ Work supported by local Basque government through IKERTU-II project,

ZE-2021/00050

MC3.5 RFQs

63

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RF TUNING ANALYSIS OF A 750 MHz CARBON RFQ FOR
MEDICAL APPLICATIONS∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB017

G. Moreno Fernández-Baíllo† , D. Gavela Pérez, P. Calvo Portela, M. León López,A. Rodríguez Páramo, J. Etxebarria, C. Oliver Amorós, J. M. Pérez Morales, CIEMAT, Madrid, Spain
J. Giner Navarro, ICMUV, Paterna, Spain
J. M. Carmona, M. Alvarado Martín, X. Arrillaga, AVS, Elgoibar, Spain
U. Etxebeste Rodríguez, Egile Mechanics S.L., Gipuzkoa, Spain
A. Lombardi, A. Grudiev, CERN, Geneva, Switzerland
Abstract
As an initial part of a future linac for hadron therapy, two
750 MHz Radio Frequency Quadrupoles (RFQs) have been
preliminarly designed by CERN, based on the compact HFRFQ model. These RFQs aim to accelerate carbon ionsfrom 15 KeV/u to 5 MeV/u. Each RFQ is composed of fourindividual modules.
Manufacturing imperfections and misalignments can result in local variations in the frequency and electromagnetic
field distribution within the RFQs. In this study, we focus on
analyzing the electromagnetic sensitivity to possible modifications in the structure of a single RFQ module. Additionally,
we evaluate how the combination of these irregularities cangenerate significant dipole errors, even when they remain
within the specified dimensional tolerances. For this purpose, electromagnetic simulations are conducted using CSTStudio.

INTRODUCTIONCIEMAT is working in the design of a carbon ion linear accelerator, the LINAC6+, for medical applications in hadron
therapy. This accelerator, still under development, aims toprovide a more precise and effective treatment against cancer cells, with a better energy modulation than current synchrotrons [1]. The initial part of the linac injector includes
two 750 MHz RFQs, to accelerate carbon ions C6+ up to
5 MeV/u, based on a compact design of the proton CERN
HF-RFQ [2]. The design and manufacturing of this kind of
RF structures is currently in progress in the framework of
Spanish innovation projects withing Spanish industry (IKERTU and CPP 03/2023 project).
This cavity, operating in the resonant TE210 mode, consists of four vanes that act as alternating voltage electrodes
RF period (Fig. 1). Each pair of adjacent electrodes has an
opposite polarization, with an absolute value of 𝑉0 cos(𝜔0 𝑡).
There are two main features of the RFQ that will enable asignificant breakthrough in the field of particle accelerator
cavities. On the one hand, the reduction in cavity length byminimizing the adiabatic bunching section. Negatively, thischaracteristic results in increased transmission loss, similar
to the proton HF-RFQ [2]. On the other hand, the introduc-tion of a trapezoidal vane modulation to improve acceleration
efficiency [3], [4]. In Table 1 the specifications of the RFQ
are shown:
Table 1: Summary of the RFQ specifications. The reduction
in values due to the use of trapezoidal vanes compared tothe standard vanes is shown in parentheses [3], [4].
Parameter

Value

Frequency
Vane Length
Module Length
RF Peak Power
Input Beam Current
Minimum Aperture
Transmission
Maxime Surface Field

749.48 MHz
4.6 m (-20%)∼ 580 mm
480 kW (-20%)
0.19 mA
0.67 mm50%
51 MV/m

RFQ cavities can be considered as a transmission line
model due to the spatial separation of the electric and magnetic fields [5]. The quadrants 𝑄1 , 𝑄2 , 𝑄3 , and 𝑄4 (seeFig. 1) can be replaced by equivalent inductance-capacitancecircuits in parallel, where 𝐶𝑖 and 𝐿𝑖 are the capacitance andinductance per unit lenght of each quadrant 𝑄𝑖 . In the caseof perfect RFQs, the capacitive and inductive impedances
are constant and equal to each other. However, if the cavity
experiences displacements between vanes or in the external
structure, the values 𝐶𝑖 and 𝐿𝑖 are affected by perturbations.
Modifications in capacitance and inductance create a mixof modes within the cavity, altering the electromagnetic
fields and creating dipole components. In the case of voltage,
it will change 𝑈 = 𝑈0 = (𝑉0 , 0, 0) to a displacement equal
to 𝑈 = 𝑈0 + 𝛿𝑈 = (𝑉0 , 0, 0) + (𝛿𝑈𝑄 , 𝛿𝑈𝑆 , 𝛿𝑈𝑇 ) [6]. The
values are defined in the basis 𝑈 = |𝑈𝑄 , 𝑈𝑆 , 𝑈𝑇 |, which is alinear combination of the inter-electrode voltages present ineach quadrant (𝐴𝑖 ) [7]:† gabriela.moreno@ciemat.es

𝐴1 − 𝐴 2 + 𝐴 3 − 𝐴 4
4
𝐴1 − 𝐴3𝑈𝑆 =2
𝐴2 − 𝐴4
𝑈𝑇 =2
assigning the appropriate sign to account for the alternatingorientation of the TE210 quadrupole mode field in the four
quadrants.

MOPB: Monday Poster Session

MOPB017∗ Work supported by local Basque government through IKERTU-II project,

ZE-2021/00050, and Spanish CDTI CPP 03/2023 project.

MC3.5 RFQs

𝑈𝑄 =

67

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STUDY OF MANUFACTURING ERRORS IN 750 MHz RFQ USINGELECTROMAGNETIC SIMULATIONS∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB018

A. Rodríguez †, P. Calvo , J. Etxebarria, G. Moreno, C. Oliver, M. León, D. Gavela,
J. M. Perez, CIEMAT, Madrid, Spain
J. M. Carmona, A. Tato, AVS, Elgoibar, Spain
Abstract
This work presents the design of Beam Position
Monitors for a 750 MHz Linac for hadrontherapy studies.
BPMs will be installed in different sections of the Linac,
operating at different energies, from the RFQ exit at 5
MeV/u to the end of the line after IH cavities at 10 MeV/u.
The BPMs will allow measurement of the beam position,phase and time of flight (tof) measurements. Therefore,
they are fundamental for commissioning and operation of
the protype hadrontherapy Linac.
In the analysis we compare the expected signal fromstripline and button BPMs using analytical and CST
models, studying the BPMs dimensions and response atdifferent energies, and BPMs sensitivity for position, phaseand tof measurements.

INTRODUCTION
The LINAC6+ is a project currently under development,with the goal of performing radiobiology studies forhadrontherapy using a Carbon 6+ beam. The Beam
Position Monitors (BPMs) are crucial diagnostics both forthe accelerator commissioning and during operation. The
BPMs will be installed at different Linac sections after the
RFQ, giving information about the beam position andphase, and allowing energy measurements through time offlight.
The LINAC6C+ will be composed of an ion source and
LEBT up to 15 keV/u , a 750 MHz RFQ up to 5 MeV/u [1]and IH cavities up to 10 MeV/u [2]. The Linac will operatewith beam pulse currents of 190 μA, with pulse durationsof 5-10 μs at repetition rates of 200-400 Hz [3]. In Table 1
the expected BPM operation parameters are described.
For the design of the BPMs we have first studied the
expected signal using analytical formulae, and thenperformed electromagnetic simulations using CST. The
analysis allows comparison of stripline and button BPM,
characterizing the expected signal for the definition ofrequirements for the amplification electronics.
Table 1: Main Operational Parameters for the BPMs
Parameter
RF Frequency
Beam Energy
Beam Pulse Current
Beam Pulse Duration
Repetition Rate

IMAGE CURRENT
When the beam passes through a Linac section an image(or wall) current is induced in its surrounding conducting
elements. If electrodes are installed, they pick-up thesignal, and with a configuration of four electrodes the beam
position can be measured.
For the estimation of the BPMs signal first the image
signal at the electrode location is estimated [4]:𝐼𝑠(𝜔) = 𝛼 ⋅𝜔 =−𝐼 (𝑔𝑟)+2
𝐼 (𝑔𝑅)⋅ 𝑠(𝜔)(1)

1 𝐼 (𝑔𝑟)⋅𝑛 𝐼 (𝑔𝑅)⋅ 𝑠in 𝑛(𝛼/2 − 𝜑) − sin 𝑛(𝛼/2 − 𝜑)(2)

The image current depends on the bunch current in thefrequency domain 𝐼(𝜔), the position of the beam(r, φ), the bean energy (γβ) the beampipe radius (R) andaperture (α). The aperture α for a stripline BPM is its width
angle, and for a button bpm of radius 𝑟 is 𝛼 = 2𝜋 ⋅ 𝑟 /4𝑅.
𝐼 (𝑥) are the modified Bessel function of order n and𝑔=
the dependence on energy.
For the LINAC6+ BPMs the expected pulse current is
190 μA with a bunched structure of σ~20 ps at 750 MHz.
Solving Eq. (1) and applying Fourier transform, the resultsin time domain are obtained. In Figure 1 we show thebunch current and its image current. For low beta beams
the signal is distorted, since the field is not transversal, andthe observed signal duration increases from σ~20 ps on the
beam to ~150 ps on the image signal.

Value
750 MHz
5-10 MeV/u
190 μA
5-10 μs
200-400 Hz

Figure 1: Bunch current and image current for a beam withpulses of 190 μA at 750 MHz and 20 ps bunches.

___________________________________________* Work supported by CPP 03/2023† angel.rodriguez|@ciemat.es.
MOPB: Monday Poster Session
MC4.1 Beam diagnostics

MOPB018
71

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DESIGN OF BPMs FOR A 750 MHz HADRONTHERAPY LINAC

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB019

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OVERVIEW OF ACCELERATING STRUCTURE
RESEARCH ACTIVITIES AT IHEP*
J. R. Zhang†, C. Meng, H. Shi, N. Gan, O. Xiao, X. Li, X. He,
X. Ma, J. Liu, D. He, Z. Zhou, J. Li, Y. Li, J. Gao
IHEP, Beijing, China
Abstract
In electron linear accelerators, the improvement of theacceleration gradient of the acceleration structure has beena continuous research topic for scientists, which can reducethe construction cost of the entire accelerator by increasing
the accelerating gradient. For the CEPC and HEPS projects
at IHEP, S-band 3 meters long and C-band 1.8 meters longaccelerating structure has been developed. The operating
frequencies are 2860 MHz, 2998.8 MHz and 5720MHz respectively. CEPC linac is 30 GeV with S & C-band structures in the TDR phase. The high-power test gradient of
S-band accelerating structure reach the 33MV/m. The
C-band structures also designed and waiting for highpower test. HEPS is 500 MeV linac injector and alreadyconditioning for one year. The maximum gradient achieved
with the beam during commissioning was approximately
26 MV/m with a beam current of 7 nC. During actual operation, it has been functioning at around 20 MV/m. The
electron beam has remained stable up to the present time.

INTRODUCTION
In an electron linear accelerator, the RF field is used toaccelerate the electron beam. The accelerating structure isa crucial component that converts the RF field energy generated by the power source into the beam energy. High-gradient accelerating structures can provide higher acceleration levels in a shorter distance, thereby enhancing the efficiency and performance of the accelerator. In other words,
they can achieve the required acceleration energy within ashorter length. That will not only save space but also reduce construction and operating costs.
The Circular Electron Positron Collider (CEPC) is alarge circular electron-positron collider project being developed by the Institute of High Energy Physics (IHEP) in
China. The injector linac of the CEPC is a 30 GeV normalconducting (NC) linear accelerator, which includes a linear
section and a 1.1 GeV damping ring (DR) [1]. In the designof the linac, an S-band structure is used before the DR, anda C-band structure is used after the DR to increase the accelerating gradient and reduce costs. Additionally, we will
focus on and develop more advanced accelerator technologies to improve the performance of the linac and reduce
construction costs.
High Energy Photon Source (HEPS) linear accelerator
operates on a 500 MeV S-band system. With the construction phase now successfully concluded, the linac can deliver a maximum stable beam current of 7 nC to the booster.
___________________________________________* Work supported by NKPSTRD & HEPS, a major national scienceand technology infrastructure in China.
† zhangjr@ihep.ac.cn
MOPB01974

DESIGN OF RF SYSTEM AND
DEVELOPMENT OF ACCELERATINGSTRUCTURES
During the Technical Design Report (TDR) phase for the
CEPC, adjustments were made to the injector linac toachieve a better balance with the booster. Compared to the
CT coil dipole magnet, the key advantages of the iron-core
dipole magnet are low cost and low power loss. In order tocontrol the production cost and power loss, the injection
linac energy of the booster is increased from 10 GeV to 30
GeV [2,3]. Even considering the increase of linac cost, theoverall price of the injection including linac and booster isstill decreasing.
The 30 GeV linac provides electron and positron beams
for the booster, with 1.1GeV damping ring for the positronbeam. The linac parameters shows in Table 1. Figure 1
shows the layout of the CEPC linac. The total length of thelinac from start to end is about 1.6 km. Thermal cathodeelectron gun is used to produces 10 nC bunch charge. Theenergy on the positron target is 4 GeV. Conventional
scheme (fixed target with FLUX) is selected for the positron source.
Table 1: CEPC Linac Parameters
Parameter

SymbolUnit

Baseline

EnergyEe-/Ee+GeV

30

Repetition rate

frep

Hz

100

Bunch charge-nC

1.5 (3)

Energy spread

σE-

1.5×10-3

Emittance

¦r

nm

6.5

Figure 1: Layout of 30 GeV CEPC linac.
The RF system includes a bunching system and main accelerating structures. The bunching system comprises of
two sub-harmonic cavities with frequencies of
158.89 MHz and 476.67 MHz, and one 2860 MHz S-band
accelerating structure. For the total 30 GeV linac, there are
MOPB: Monday Poster Session
MC4.7 Room temperature RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB021

Z. Mi †1, M. Liu1, W. Zhou1, W. Pan1, R. Ge1, C. Zhang1, F. He1, J. Zhai1, M. Xu1
Institute of High Energy Physics, CAS, Beijing, China1also at University of Chinese Academy of Sciences, Beijing, China
Abstract
The China Spallation Neutron Source phase II (CSNSII) upgrade design will increase the total beam power from100 kW to 500 kW and boost the beam energy from80 MeV to 300 MeV in the linac by adding a superconducting linear accelerator to the existing accelerator complex.
The double spoke resonator is used in the energy range of
80 MeV to 165 MeV. To compensate the frequency change
due to manufacturing uncertainty, Lorentz force, beamloading, He pressure and microphonics, a new type tuner isdesigned for the double spoke superconducting cavity. The
tuner is mounted on the side of the cavity, and each module
contains two tuner systems. In this paper, the structure andworking principle of the tuner are designed and analysed,
also the testing result of the tuner with the double spoke
Resonator and cryomodule prototypes are introduced.

Figure 1: 324 MHz double spoke cavity 3D model.

INTRODUCTION
The baseline and main parameters for upgrade SRF system of CSNS-II have been public [1, 2]. IHEP is developing 324 MHz double superconducting RF cavities for
CSNS-II, the structure is shown in Fig. 1. In order to increase the beam power from 80 MeV to 165 MeV, and alsowith the beam peak current increase from 15 mA to 50 mA,
twenty double Spoke superconducting cavities with β0=0.5
are used, as the scheme shown in Fig. 2. Each cryomodule
contains two 324 MHz superconducting cavities, for a totalof ten this cryomodules. The spoke cavity operates in pulse
mode and is mainly affected by Lorentz force, to adjust thecavity resonance frequency to the accelerator frequency
during operation is essential to the RF system stable andhave a perfect transmission of the radiofrequency power tothe beam, also reduce reflection power. The cavity parameters as shown in Table 1, to meet the requirements of
324 MHz double Spoke cavities, newly tuner system is designed. Two type tuners have been designed and test for the
performance verification. Due to the lever tuner are widelyused for SRF cavity to tuning frequency for install andmaintains easily, lever tuner has been chosen as the basic
structure. And adopts the structure of motor tuner (slowtuning) and piezo tuner (fast tuning). Assembled the two
type tuners and cavity in the cryostat, and completed thewarm temperature (300 K) test and cold test (2 K). The research objectives include verify the tuner’s design andoverall structure, evaluate its performance at different temperatures, and assess its effectiveness in achieving the desired tuning capabilities___________________________________________* Work supported by China spallation resources phase II project & Youthinnovation promotion association CAS† mizh@ihep.ac.cn
MOPB: Monday Poster Session
MC4.8 Superconducting RF

Figure 2: CSNS -II linear accelerator upgrade scheme.
Table 1: Parameters of Double Spoke Cavity
Parameters

Value

Units

Frequency
Aperture
Operatingtemperature
Β0
Ep/Eacc
Bp/Eacc
G
R/Q
Operating gradientOperating frequency
Cavity stiffness
Tuning sensitivity
Kl (tow beam
pipe free)Kl(one beam
pipe free)df/dp
Frequency

324
50
2

MHz
mm
K

0.5
4.1
9.2
120
410
7.3

--mT/(MV/m)
Ω
Ω
MV/m

25

Hz

~10

N/um

100

kHz/mm-12.54-10.47

Hz/(MV/m)2
Hz/(MV/m)2-0.773324

Hz/mbarMHz

MOPB02177

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DESIGN AND TEST OF DOUBLE SPOKE SUPERCONDUCTING CAVITY
TUNER FOR CSNS-II *32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB023

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ADVANCEMENTS IN Nb3 Sn GROWTH FOR SRF TECHNOLOGY
L. Shpani∗ , M. U. Liepe, Cornell University, Ithaca, NY
V. Do, H. Lew-Kiedrowska, S. J. Sibener, C. Wang, University of Chicago, Chicago, IL
Abstract
Nb3 Sn is the most promising alternative material for the
future of superconducting radio-frequency (SRF) technology, steadily advancing towards practical applications. Having a critical temperature twice that of niobium, Nb3 Sn
offers the potential for developing smaller, more powerful,and more efficient accelerators. We have designed a comprehensive study to synthesize and characterize substrate
treatments at nucleation temperatures following the thermal
vapor diffusion growth process to improve the uniformity of
Nb3 Sn coatings, pushing its performance closer to fundamental limits.

INTRODUCTION
Having a critical temperature two times that of Nb and apotential to achieve twice the accelerating fields comparedto Nb cavities, Nb3 Sn is the most promising alternative material for the future of SRF technology [1–4]. Nb3 Sn cavities
can reach high quality factors (>1010 ) at ∼ 4 K liquid heliumtemperatures, and thus can be operated efficiently at 4 K as
opposed to niobium cavities which are typically operated at2K [4]. Employing Nb3 Sn cavities will significantly reducethe cost and complexity of SRF technology, making SRF
technology accessible at a smaller scale and to a variety of
applications, such as wastewater treatment, medical isotope
production, and ultrafast electron diffraction [1]. While there
has been significant progress in research and development of
Nb3 Sn cavities, there still remain practical challenges in thesynthesis of this material that need to be addressed for the
performance of this material to come closer to its theoreticallimitations. The state of the art growth method for Nb3 Sn
cavities is thermal vapor diffusion, where a Nb cavity is put
inside a high vacuum furnace along with a tin source and anucleating agent of tin chloride (SnCl2 ) and heated at hightemperatures (> 900 ∘ C) where the A15 Nb3 Sn structureformation is thermodynamically favorable. More details of
the coating process can be found in [2, 3, 5].
Synthesizing a uniform layer of the right stoichiometryon the complex cavity surface is crucial for achieving highquality factors and high accelerating gradients. A common
culprit for premature cavity quenches and degraded cavity
performance are tin depleted regions [3–5]. There are a
few ways that we can help avoid these tin depleted regions.
Growing an amorphous Nb2 O5 layer on the Nb substrate
before Nb3 Sn growth has been shown to result in less tin
depleted regions compared to the native oxide [5]. Recent
studies have shown that altering this anodic pentoxide canhelp promote more uniform nucleation of tin at early stagesof growth [2].
∗ ls936@cornell.edu

MOPB02380

The main hypotheses to describe the mechanism behind
the role of the oxide are the increased surface area of theamorphous Nb2 O5 film compared to the native oxide, andthe thermodynamic role of oxygen in aiding the initial stagesof the alloying process [6].

Anodic Growth of Niobium Oxide
Anodic niobium oxides are well studied outside the fieldof SRF and accelerator physics for a variety of applicationsin other disciplines such as solar cells and chemical sensing[7]. When niobium is made the anode of electrolytic cell,anodic oxidation is one of several reactions that can occur incompetition with other reactions such as anodic dissolution
or oxygen evolution [8]. The mechanism behind this anodic
oxide growth is illustrated in in Fig. 1. The final properties,
chemistry, and morphology of the anodic Nb2 O5 are influenced by the operating conditions, namely the temperature,
current density, terminating voltage, the pH and chemicalcomposition of the electrolyte.

Figure 1: Simplified illustration of the anodic pentoxide
growth. First, the barrier oxide layer growth (right) happensat the oxide/electrolyte interface through the outward migration of Nb5+ cations, and at the oxide/metal interface
through the inwards migration of O2− anions. If the oxide
is soluble in the electrolyte, a porous oxide layer is formedat the oxide/electrolyte interface (left).
When the oxide is soluble in the electrolyte, we can synthesize porous oxide surfaces at the electrolyte/oxide interface.
Niobium oxide is attacked by HF and by alkali electrolytes
with pH ≥ 14 [8]. Studies have been done on anodic Nb2 O5
with various growth conditions and porosity of the surface of
these films have been characterized and a voltage-thickness
relationship has been established [7–9].
The study done at Cornell University [5] found that anodizing Nb substrates in 10%w/w NaOH with terminating
voltages of 15, 30, and 50 V all resulted in more uniform
Nb3 Sn layer coverage compared to the native oxide, butthere was no significant difference (to the limits of EDX
measurement) between these three voltages . Another study[10] reported tin droplets to be bigger and more sparsely
distributed when anodized in NH4 OH at 50 V as opposed
to 30 V. This discrepancy could be explained by the use ofdifferent electrolytes and potentially different current density
limits.
MOPB: Monday Poster Session
MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB024

N. Verboncoeur† , A. Holic, M. Liepe, T. Oseroff, R. D. Porter‡ , J. Sears, L. Shpani
Cornell Laboratory for Accelerator based ScienceS and Education (CLASSE), Ithaca, NY, USA
Abstract
The Cornell High Pulsed Power Sample Host Cavity (CHPPSHC) is a new system designed to measure the superheating field of candidate superconducting RF (SRF) materials,
giving insight into their operational limits. This system isdesigned to reach peak magnetic fields of up to 0.5 T in only
a few microseconds, allowing us to achieve a purer magnetic field quench on the sample. We present an overview
of the CHPPSHC system and proof of principle data from aniobium sample.

INTRODUCTION
Improving the accelerating gradient, 𝐸𝑎𝑐𝑐 , of superconducting radio-frequency (SRF) cavities is a desirable goal
for the next generation of accelerators. The upper limit on
𝐸𝑎𝑐𝑐 for a given material is set by its superheating field, 𝐵𝑆𝐻 ,and the cavity geometry. Niobium cavities are the current
standard and has a 𝐵𝑆𝐻 of ∼ 200 mT corresponding to a maximum 𝐸𝑎𝑐𝑐 of ∼ 50 MV/m in an elliptical cavity [1]. The
SRF community has been investigating other materials [2,3] including Nb3 Sn, which is predicted to have a 𝐵𝑆𝐻 of ∼400 mT [4, 5]. This corresponds to an upper limit on 𝐸𝑎𝑐𝑐of ∼ 100 MV/m.
To date, there has not been satisfying experimental measurements of Nb3 Sn’s superheating field. Previous attempts
have been made, however these experiments have been
severely limited by thermal effects. The superheating field
is an extremely temperature-dependent property, so even asmall amount of heating can lower the quench field. Here,
we explore the Cornell High Pulsed Power Sample Host
Cavity (CHPPSHC), a sample host structure specifically designed to measure the limiting magnetic fields of candidate
SRF material samples [6, 7].

THE CORNELL HIGH PULSED POWER
SAMPLE HOST CAVITYThe CHPPSHC must be able to reach fields exceeding thepredicted 𝐵𝑆𝐻 of Nb3 Sn fast enough that heating does nothave a significant effect on the measurement. The CHPPSHC
utilizes a 1 MW klystron with pulse lengths on the order of
10 µs. Past experiments at Cornell were done with 1.3 GHz
elliptical cavities, but maximum fields were thermally limited due to pulse lengths of 50 - 100 µs [1]. The CHPPSHC’s
geometry is designed to charge quickly by exploiting fieldenhancement along the sharp edge of the sample. A simulation of the magnetic field in the cavity is shown in Fig. 1.
∗ Supported by U.S. Department of Energy Grant No DE-SC0008431† nmv39@cornell.edu‡ Now at SLAC, Menlo Park, California, USA

MOPB: Monday Poster Session
MC4.8 Superconducting RF

Figure 1: Simulation of peak magnetic fields along 𝑥 = 0(left) and 𝑧 = 0 (right) planes of the CHPPSHC in CST
Microwave Studio. The design exploits field enhancement
to reach significantly higher peak fields on the sample edge.
An upper bound of 1 × 105 A/m was set on the color scale
for visibility purposes. The peak field on the sample is ∼4 × 105 A/m corresponding to ∼ 500 mT.
The peak field on the sample edge is enhanced by a factorof 500 due to this effect, which allows the system to reach amaximum field of ∼ 500 mT in only ∼10 µs [6].
The simulation also calculates the quality factors of various components of the system. While superconducting,the sample accounts for less than 0.001 % of losses. Whenthe sample is normal conducting at 300 K, the losses on thesample reach ∼ 70 % of losses. The resulting sharp drop in
the system’s 𝑄0 is large enough that it will be evident in RF
power data when the sample has quenched.

PULSED RF DATA
Before investigating Nb3 Sn, baseline data for a niobium
sample is necessary to ensure that quench information canbe accurately extracted from our measurement results. A
niobium sample was prepared using the same processes
applied to a niobium cavity, receiving a bulk chemical polish,
electropolishing, and a 5 hr 800 C bake. The sample wascleaned with DI water in a class 100 cleanroom before being
assembled into the copper host structure.
The host cavity is tested in helium over a temperature
range from 2 K to 9 K and driven by a 1 MW klystron. Before taking pulsed data, a system calibration is done in continuous wave (CW) operation to determine the loaded quality
factor, 𝑄𝐿 , the coupling, 𝛽, and field calibration. In Fig. 2,
an example pulsed operation data point is shown. 𝐵𝑝𝑘 is
calculated from the RF data using the results of the CW
calibration and the CST simulation.
Figure 2 shows a pulse that exhibits “overfilling” behavior
where the cavity continues to fill despite the sample quenching. This makes it more difficult to accurately identify thequench field as the underlying mechanisms become more
complex.
MOPB024
83

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HIGH PULSED POWER MEASUREMENTS OF SUPERHEATING FIELDSFOR SRF MATERIALS∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB026

DESIGN OF A QUADRIPARTITE WAKEFIELD STRUCTURE
FOR FREE ELECTRON LASER APPLICATIONS
Y. Ji1 , C. Lei1 , J. Shao1, , Y. Yu1 , J. Sun2 , Z. Li1 , L. He1 , H. Wang1 ,J. Wei1 , W. Wei1 , W. Wang1 , J. Yang2 , W. Zhang2 , X. Yang2
1
Institute of Advanced Science Facilities, Shenzhen, China
2
Dalian Institute of Chemical Physics, Dalian, China
Abstract
Wakefield structures are broadly employed in free electron
laser (FEL) facilities for beam manipulation. Compared withcylindrical geometries, planar structures are typically preferred due to their increased flexibility, allowing for tunable
wakefield strength through gap adjustment. However, theseplanar configurations can induce time-dependent quadrupole
wakefields, which require careful compensation in various
applications. To address this issue, we propose a novel structure design incorporating four identical corrugated elements
which are independently controllable. By adjusting the gaps
between orthogonal pairs, the quadrupole wakefield can beeither fully compensated to avoid emittance growth or significantly amplified to enhance beam mismatch for slice lasing
control. This manuscript presents both the physical andmechanical design of the proposed structure, as well as theplanned proof-of-principle experiment.

INTRODUCTION
Wakefields are induced when a charged bunch traverses
a corrugated or dielectric pipe. Structure-based wakefield
acceleration represents a promising approach to achieve gradients significantly higher than those attained by conventional techniques [1–3]. Furthermore, wakefield have been
demonstrated to be effective tools for beam manipulation in
FELs, where the short-range wakefield from the bunch head
can alter the longitudinal or transverse momentum of thetail [4–18]. Initially, wakefield structures were employed in
FELs as dechirpers to mitigate the linear energy chirp introduced for magnetic bunch compression [4, 5, 7]. Since then,these structures have been adapted for a broader range of applications, such as passive linearization [6, 13], slice lasing
control [8, 10–12, 14, 15], and passive deflection [9, 17, 18].
The Shenzhen Superconducting Soft X-Ray Free-Electron
Laser (S3 FEL) is a newly proposed, high repetition-rate
FEL facility featuring multiple undulator lines that lase in
the 1–30 nm range [19]. Wakefield structures are underdevelopment to serve as dechirpers and as key components
for advanced FEL modes. Their performance is crucial toachieving high lasing quality in S3 FEL.
Most FEL facilities apply planar structures with two corrugated plates, where the longitudinal wakefield strength
can be adjusted by varying the gap. However, quadrupole
wakefield is introduced in addition to the longitudinal wakefield due to the asymmetric geometry. The time-dependent

Figure 1: Schematic layout of the quadripartite wakefieldstructure.

quadrupole wakefield can cause beam mismatch and emittance growth, which usually require compensation by placing two pairs of plates orthogonally and maintaining nearly
symmetric average 𝛽 functions throughout the structures [7].
Conversely, purposely enhancing beam mismatch via thequadrupole wakefield can be exploited for slice lasing control, by individually matching the slices into different undulators [10, 11]. Consequently, it would be desirable tointroduce a structure that provides flexible and independent
control of both longitudinal and quadrupole wakefield.
Therefore, we propose a novel wakefield structure consisting of four identical elements. By adjusting the gaps
between orthogonal pairs, the quadrupole wakefield can beeither fully compensated or significantly amplified, while
the impact to the longitudinal wakefield is moderate. Suchdesign allows for flexible manipulation of bunch slice properties for various applications.

PHYSICAL DESIGN
The quadripartite wakefield structure comprises four identical corrugated plates, each independently controlled by apair of high-precision motors, as illustrated in Fig. 1. The∗ shaojiahang@mail.iasf.ac.cn

MOPB: Monday Poster Session
MC2.4 FELs

MOPB026
87

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∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB027

A. Tropp, P. Gu, C. Christou†
Diamond Light Source, Oxfordshire, UK
Abstract
The Linac for Diamond Light Source has been runningwith two 3 GHz klystrons, powering two 5.2m-long accelerating structures to deliver 100 MeV electron beam since
the start of operation. By introducing a SLED RF pulse
compressor system to generate a pulse capable to powerboth structures from one klystron, redundancy and reliability will be improved. With a 5 µs total pulse, it is possible
to charge the SLED cavities for 4 µs and generate a highpeak pulse for the last 1 µs able to power both structures.
An arbitrary waveform generator function was implemented in digital low-level RF to generate a flat top pulse,which can be utilized for both single bunch and multibunch operation. Details of the waveguide network, lowlevel RF design and high-power operation will be described. Results from full energy operation will also be
shown.

splits the power between the two accelerating structures
AS1 and AS2. By changing the switches both klystrons canalso be used as in the old configuration.
A High-power RF window capable of withstanding apeak power of 70 MW was also installed directly after the
SLED, see Fig. 2. This window is based on the PAL design[1], and the design change from 2856 MHz to 2998 MHz
lowered the power limit slightly.
The final installation was done in March 2024 and allowed carrying out high power tests.

LINAC MODIFICATIONS
Diamonds original Linac configuration can be seenin Fig. 1 on the left. To use both klystrons to power the
RF pulse compressor, a new configuration of the
waveguide had to be designed. The first design with
SLED did not use compressed RF pulse for the bunching
structures as can be seen in the middle configurationlayout in Fig. 1. This was later changed, and the final
design layout was made, shown on the right side of Fig. 1.

Figure 2: SLED and window assembly inside Linac.

DIGITAL LOW-LEVEL RF
The DLLRF is based on the Micro Telecommunications
Computing Architecture (MicroTCA) standard. It was chosen for its reliability, modularity and scalability. The
DLLRF consists of a 2U MTCA.4 chassis, a MCH, an
AMC computer board, a Struck SIS8300-KU card and a
Struck DWC8VM1 RTM with supporting clock/local oscillator (LO)/reference generation RF circuits, see Fig. 3.

Figure 1: Linac configurations from start to finish of project. Initial without SLED (left), Intermediate (middle), final design (right).
This design allows either of the klystrons to power thepulse compressor by using two RF switches SW1 andSW2. After the pulse compressor the power will first be
split to the bunching structures FBU and PBU. After thisthe remaining power goes through a splitter SP3 which___________________________________________† Present address DESY, Hamburg, Germany

Figure 3: Schematic for the digital low-level RF.

MOPB: Monday Poster Session

MOPB027

MC2.7 Synchrotron light sources

91

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SINGLE BUNCH AND MULTI BUNCH OPERATION WITH SINGLEKLYSTRON USING A PROGRAMMABLE SLED SYSTEM

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB028

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C-BAND RF SYSTEM FOR THE SAPS TEST BENCH
Hui Zhang1, Zhencheng Mu2, Hexin Wang2, Zhexin Xie2, Linyan Rong2, Bo Wang2,
Maliang Wan2, Shimin Jiang2
1
Spallation Neutron Source Science Center, Dongguan, China
2
Institute of High Energy Physics, Beijing, China
Abstract
This work describes a C-band RF system for the SAPS
(Southern Advanced Photon Source of China) test benchlinear accelerator. SAPS' RF testing system comprises of aphotocathode electron gun and a 2-metre-long equal gradient acceleration device. The klystron power source delivers
energy to the photocathode electron gun and the travellingwave acceleration structure, respectively. Test the photocathode electron gun first, followed by the travelling wave
acceleration structure. We investigated a short-pulse Cband spherical pulse compressor. The photocathode electron gun's preliminary high-power testing is now complete.

INTRODUCTION
To improve the beam quality of photocathode microwave electron guns, increase the gradient inside the electron gun to lower heat and space charge emissivity. The
photocathode electron gun cavity is designed to achieve an
acceleration gradient of 150 MV/m.A 2-meter-long travelling wave acceleration structure is put at the back end of
the photocathode electron gun to increase the energy andstabilise the emissivity of the electron beam emitted by thegun.
The RF system's function is to deliver enough power tothe electron gun cavity to achieve a gradient of 150 MV/m,
as well as RF power to the travelling wave acceleration
structure to ensure that its gradient satisfies the design criteria. Figure 1 shows the layout design for the electron gun
and accelerator tube.

Figure 2: Composition of C-band RF power source.

Figure 3: RF system schematic diagram.

Klystron

Figure 1: Layout of electron gun and accelerator tube.

RF SYSTEM
The components of the C-band RF system include a circulator, directional couplers, rectangular waveguides, aspherical pulse compressor, and more. Figure 2 display the
C-band RF power source system's composition diagram.
The klystron, circulator, and pulse compressor which are
positioned in the system as seen in Fig. 3 are the most important parts of the RF power system.

MOPB028
94

The traveling wave acceleration structure and the photocathode electron gun in the SAPS experimental device will
each require one klystron with a 20 MW output power.
High throughput electron optical system, highly dependable microwave output system, and high-efficiency beamwave interaction system are all features of C-band klystron.
The klystron mainly comprises an electron optics system,a beam-wave interaction section, and a collector [1]. The
designed klystron, with a working frequency of 5712 MHz,peak power of 50 MW, repetition rate of 50 Hz, and pulse
width of 2.5 μs, satisfies the performance criteria of highgradient acceleration devices. Operational stability was
taken into account when testing the klystron, and an RF
pulse width of 1.2 μs was employed.
When the klystron was tested with an RF pulse width of
1.2 μs and a repetition rate of 5 Hz, the output power
reached 45 MW. Figure 4 shows the power display.

MOPB: Monday Poster Session
MC4.6 RF power sources and power couplers

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB029

Qiyu Kong∗ 1 , Huachang Liu1,2 , Jun Peng1,2
Spallation Neutron Source Science Center, Dongguan, China1also at Institute of High Energy Physics, Chinese Academy of Sciences (CAS), Beijing, China2also at University of Chinese Academy of Sciences, Beijing, China
Abstract
The China Spallation Neutron Source (CSNS) has been
operating at a stable beam power of 160 kW since March
2024, marking a significant 60% increase from its original design capacity. The ongoing CSNS upgrading project,known as CSNS-II. As part of this upgrade, a versatile
Medium Energy Beam Transport (MEBT) system has been
meticulously studied and redesigned to meet the stringent requirements for beam control in the presence of strong spacecharge effects. The MEBT system boasts several key functions and features, including beam chopping for optimizing
beam structure, scrapers for confining and removing beam
halo particles. Detailed studies on beam performance, in
conjunction with the main linac, have been carried out andare presented in this article.

INTRODUCTION
The China Spallation Neutron Source (CSNS) leverages
a high-energy proton accelerator to generate neutrons fora diverse array of scientific investigations [1]. The highenergy proton accelerator complex initiates with the 81 MeV
H− linear accelerator, consists of a 50 keV H− ion source,a low energy beam transport line (LEBT), a 3 MeV Radio Frequency Quadrupole (RFQ), a medium energy beamtransport line (MEBT), an 81 MeV Alvarez-type Drift Tube
Linac (DTL) [2]. Then, H− ion is stripping injected into
rapid cycling synchrotron (RCS), where they are accelerated
to 1.6 GeV.
The ongoing upgrade of the CSNS, known as CSNS-II,
aims to enhance the linac peak current to 50 mA while theenergy increase to 300 MeV, facilitated by a superconducting
accelerator featuring Double-Spoke Resonators (DSR) [3]and Elliptical Resonators (EllipR). The layout of the linac
in CSNS-II is illustrated in Fig. 1. Upon the successful
completion of this upgrade, CSNS-II is poised to become
the pioneering user open facility to deploy a superconducting
linac as an RCS injector.
Table 1: The Main Parameters of the CSNS Linac in Phase-I
and Phase-II
Parameter

Phase-I

Phase-II

Output energy (MeV)
Peak current (mA)
Repetition rate (Hz)RF frequency (MHz)Duty factor (%)

81
15
25
324
0.625

300
50
50
324&648
1.25∗ kongqy@ihep.ac.cn

MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

Figure 1: The layout of linac in CSNS-II.
The MEBT currently in operation at CSNS underwent
joint commissioning with the DTL in 2018, at an energy
level of approximately 3 MeV, which for high-intensity beam
is a section dominated by space charge effect, making emittance growth seemingly inevitable. However, the functions
it possesses are relatively simple and may not suffice to address the challenges posed by increased intensity, including
emittance growth. In response to these evolving requirements, a series of research initiatives have been undertaken
to develop a multi-functional MEBT dynamics scheme tailored to meet the demands of the CSNS-II project. This
innovative approach aims to enhance the capabilities of the
MEBT system to effectively manage emittance growth andother associated challenges arising from the intensified beam
currents, thereby ensuring the continued success and optimal
performance of the CSNS-II facility.

DESIGN PHILOSOPHY ANDCONSIDERATIONS
In high-intensity accelerator facilities, the damage causedby beam losses due to various factors should be kept as low
as possible along the linac, typically adhering to an acceptable threshold of 1 W/m for majority high-power particle
accelerators [4]. Among all kinds of different possible beamloss sources in CSNS-II, the beam loss existing in MEBT
or can be solved in MEBT mainly has the following threemechanisms:• The linac in CSNS is equipped with a beam chopper at
the LEBT with approximately a 20 ns rising edge [5].
It is important to note that the rising edge comprises
several micro-pulses that are not entirely chopped.
• With CSNS-II operating at a beam current approximately five times higher than the existing facility, it is
crucial to optimize beam halo at the entrance of the
DTL.

CHOPPER SYSTEM
A pre-chopper in LEBT together with a chopper in MEBT
is an effective solution to mitigate beam loss as in the SNS [6].
MOPB029
97

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AN ALTERNATIVE DESIGN SCHEME FOR CSNS-II MEBT DYNAMICS

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB030

Qiyu Kong∗ 1 , Huachang Liu1,2 , Jun Peng1,2
Spallation Neutron Source Science Center, Dongguan, China1also at Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China2also at University of Chinese Academy of Sciences, Beijing, China
Abstract
The CSNS consists of an H− linac as injector, the interaction of the residual gas with H− particles will strip theelectrons to produce associated protons within the LEBT,
which follow the H− into the subsequent accelerating structure. In order to avoid the adverse effects of proton loss on
the device, the feasibility of employing a bump for associatedproton separation at the MEBT was investigated firstly using
multiparticle tracking simulations. Beam experiment was
carried out in the existing CSNS MEBT device, in which
the transverse profile signals of the associated protons wereobserved. Intensity of the associated proton with and without the bump separation are compared downstream the DTL,
which proves bump separation is an effective method for theremoval of associated protons. The simulation and experimental results can provide scheme references for solving theassociated proton problem faced in CSNS-II.

INTRODUCTION
The China Spallation Neutron Source (CSNS) leverages
a high-energy proton accelerator to generate neutrons fora diverse array of scientific investigations [1]. The proton
accelerator complex presently consists of an 81 MeV H−
linear accelerator and a 1.6 GeV Rapid Cycling Synchrotron(RCS), as shown in Fig. 1. The linac consists of a 50 keV
H− ion source, a low energy beam transport line (LEBT), a
3 MeV Radio Frequency Quadrupole (RFQ), a medium energy beam transport line (MEBT), an 81 MeV Alvarez-type
Drift Tube Linac (DTL) [2]. The H− linac is an injector of
RCS, and the charge-exchange injection is adopted to mitigate the space-charge effects. Protons are finally extracted
to the target where generates neutron.

Generation of Associated Proton
H2 gas flows from the ion source into vacuum pumps in
LEBT, H2 gas is ionized to positive ion such as H+2 after
colliding with H− particles to neutralize space charge force.
A small fraction of H+ and H0 are generated by electron
stripping of H− particles with residual gas [3]. The stripping
process is described by Eqs. (1a)-(1c) [4]:(1a)𝐻− + 𝑁 → 𝐻0 + 𝑋
𝐻0 + 𝑁 → 𝐻+ + 𝑋

1

𝐻 − + 𝑁 → 𝐻 + + 𝑋2 ,

(1b)
(1c)

where N is the remnant gas molecule, and 𝑋, 𝑋1 , 𝑋2 are theother products.

Transportation of Associated Proton
Processes and protons have been observed in other facilities, such as SNS and LAMPF, protons will be absorbed
by electrodes of quadrupoles in LEBT immediately. However, CSNS adopts solenoids focusing for LEBT to mitigate
the emittance growth with the help of space-charge neutralization effect. In that case, a substantial fraction of the H+
will reach the RFQ and gradually bunched around the RFphase shifted by 180 degrees with respect to the phase of
the H− bunch. Even worst, H+ particles can be eventually
accelerated to the same energy with H− of 3 MeV as they
have almost the same charge-to-mass ratio with opposite
charge. According to the particle tracking simulation, H+
can transport through the MEBT and captured by DTL. Finally, H+ will be accelerated to 80 MeV, because there is noRF frequency jump within MEBT and DTL. 80 MeV H+ isdeflected to Associated Proton beam Experiment Platform(APEP) which is opposite to that of H− [5].

Considerations for Associated Proton Removal

Figure 1: The layout of proton accelerator in CSNS.

∗ kongqy@ihep.ac.cn

MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

The ongoing upgrade of the CSNS, known as CSNS-II,
aims to enhance the linac peak current to 50 mA while theenergy increase to 300 MeV, facilitated by a superconducting
accelerator featuring Double-Spoke Resonators (DSR) [6]and Elliptical Resonators (EllipR). Most importantly, theElliptical Resonators operate at RF frequency of 648 MHz,
which is twice of the DTL and RFQ. In that case, associated H+ will be lost in resonators of 648 MHz. In order toavoid contamination of the superconducting resonators, theremoval of associated protons generated by residual gas stripping should be considered in advance. Series of researchand experiments have been conducted.
MOPB030
101

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SIMULATION AND EXPERIMENT STUDY OF PROTON
GENERATED BY RESIDUAL GAS STRIPPING IN CSNS

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB032

M. Trovò∗ , N. Shafqat, F. Gelmetti, M. Milloch, A. Milocco
Elettra Sincrotrone Trieste S.C.p.A., Trieste, Italy
R. Fortunati, R. Zennaro, Paul Scherrer Institute (PSI), Villigen, Switzerland
Abstract
FERMI is the seeded free electron laser (FEL) user facility
at Elettra laboratory in Trieste, operating in the VUV - soft
X-ray spectral range. In order to extend the FEL radiation
to shorter wavelengths, an energy increase from 1.5 GeV to
2.0 GeV is required in the linear accelerator (linac). This
result is achievable by replacing the present old sections
with the newly designed accelerating sections that can workat high gradient with lower transverse wakefields. A new
high-gradient (HG) module was build and installed at the
FERMI linac. We report here the recent experience on theconditioning and the results on the e-beam energy gain in
operation.

INTRODUCTION
The FERMI FEL, located at the Elettra Sincrotrone research center in Trieste, Italy is the 4th generation lightsource operating in Extreme-Ultraviolet (EUV) to the soft
X-rays range. FERMI is presently driven by a 1.5 GeV, Sband normal conducting linear accelerator (linac), outlinedin Fig. 1.

Figure 2: Sketch of the FERMI upgrade plan unit.

one deflector at K15 increasing the beam energy to 1.7 GeV.
In the next phase, 14 new HG structures would replace thepresent BTW sections reaching the final goal of 2.0 GeV.
The first 3.0 m HG structure was conditioned and high-power
tested at the cavity test facility of Elettra from May 2022 toAugust 2022. After receiving the 2nd HG structure first HG
module was installed at FERMI linac during the summer
shutdown in September 2022 for commissioning with thebeam. Since that time the K15 operation is characterized bya rotation between conditioning mode and acceleration foruser operations.

BRIEF UPGRADE PLAN OVERVIEW
Figure 1: FERMI FEL linac layout (cartoon not to scale).
The upgrade plan of the FERMI aims to extend the FEL
wavelength range to cover the nitrogen and oxygen K-edge byincreasing the electron beam energy up to 2.0 GeV and thepeak current greater than 1 kA [1]. The upgrade plans the replacement of the old accelerating sections, starting from theseven, 6.4 m long, Backward Travelling Wave (BTW) structures in the high energy part of the linac (L3 and L4) which
are limited presently to a maximum gradient of 24 MV/m.
These BTW structures would be replaced with the newly
designed HG modules (one HG module consists of two HG
structures with length of 3.0 m each) that are designed tooperate reliably up to an accelerating gradient of 30 MV/mas shown in Fig. 2 [2].
This energy upgrade will enable the FERMI to generate
the photon beam up to one keV energy. In the first step, twosuch new HG structures are installed in place of S0a and∗ mauro.trovo@elettra.eu

MOPB: Monday Poster Session
MC2.2 Electron linac projects

The HG structures are constant gradient type accelerating structures operating in 2𝜋/3 phase advance mode [3, 4].
These HG structures are designed to operate reliably at anaccelerating gradient of 30 MV/m with a very low breakdown rate (BDR) with low wakefields. The HG structures
are fed using a customized version of duel-fed EC-type couplers as they have lower surface fields as compared to their
MC counterparts [5]. All the geometrical parameters of anaccelerating cell are summarised in Table 1.
A short prototype was built at Paul Scherrer Institute (PSI)
in Switzerland with the aim to verify the feasibility and reliability of the upgrade. The short prototype was fabricatedusing a technique developed at PSI which produces a tuningfree structure by adhering to very tight tolerances [6]. A
high-power S-band test facility with the BOC type pulse
compressor and National Instrument (NI) diagnostic hardware was commissioned at Elettra for conditioning and highpower testing of the short prototype [7]. The complete history of conditioning and high-power operation along withthe exhaustive post-processing of the conditioning data iscovered in [8].
MOPB032
105

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RECENT RESULTS OF THE HIGH GRADIENT S-BAND
ACCELERATING MODULE FOR FERMI ENERGY UPGRADE

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB033

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TRANSVERSE BEAM DYNAMICS SIMULATIONS BENCHMARKED WITHESS BILBAO INJECTOR MEASUREMENTS FOR ISOLDE ISRS PROJECT∗
D. Fernández Cañoto† , K. Altenmüller, I. Bustinduy, S. Masa, R. Miracoli, J. L. Muñoz,
S. Varnasseri, ESS Bilbao Consortium, Zamudio, Spain
Abstract
A multi-harmonic buncher cavity, MHB, is being designed by ESS Bilbao for the HIE-ISOLDE ISRS project at
CERN, to bunch beam pulses with 5 keV/u input energy. The
MHB will be tested with the ESS Bilbao light-ion injector.
Transverse beam dynamics simulations were carried out toanalyse preliminary measurements from hydrogen beams
produced at 5 and 10 kV. Results have demonstrated thatESS Bilbao injector can produce 𝐻 + and 𝐻2+ beams with
5 keV/u, for an optimum characterization of the MHB cavity.

INTRODUCTION
A multiharmonic buncher cavity, MHB, will be installed
before the HIE-ISOLDE RFQ to bunch beam pulses witha 5 keV/u input energy or 𝛽 = 0.00328 at 10% of RF frequency [1]. The MHB will consist of two copper electrodes
with 20 mm bore diameter installed inside a cross shaped
vessel [2]. The cavity designed by ESS Bilbao will be tested
with ESS Bilbao injector. This injector was designed foran extraction voltage of 45 kV and consists of a 2.7 GHz
Electron Cyclotron Resonance (ECR) ion source, and a Low
Energy Beam Transport line, LEBT [3].
Beams required for MHB characterization can be produced with ESS Bilbao injector using 𝐻 + accelerated at
5 kV or 𝐻2+ at 10 kV, but due to the fact that both extraction
voltages are far from ideal injector configurations, preliminary analysis of measurements were necessary. Cationsof 𝐻 + , 𝐻2+ , and 𝐻3+ in different ratios are formed from 𝐻2molecules depending on ionization energy, which characteristics would lay on ECR parameters like gas pressure,magnetic field configuration, or microwave power [4]. Additionally, identification and control of any beam species areimportant for proton therapy, spallation sources, or particle
physics applications [5].

LEBT LAYOUT
Beam dynamics simulations are performed throughout
LEBT, which layout with main longitudinal positions, 𝑍 𝑝𝑜𝑠 ,and bore diameters, Φ, is shown in Fig. 1. The LEBT consists of a 45 kV extraction column, two solenoid magnets,
𝑆𝑂 𝐿1 and 𝑆𝑂 𝐿2, and four vessels for allocation of beamdiagnostics. Beam currents are measured with the following
current transformers: ACCT1 positioned before 𝑆𝑂 𝐿1 and
ACCT2 after 𝑆𝑂 𝐿2; ACCT3 and ACCT4 after a 20 mm diameter collimator, 𝐶𝑂 𝐿 20 , being separated by a Φ = 63 mm
diameter drift pipe 210 mm long. The MHB system will
∗ Project funded by Spain Government under grant agreement Experiment

ISRS-ISOLDE (BOE-A-2023-16885).

be installed in between ACCT3 and ACCT4. The MHB
electrodes will have the same diameter as 𝐶𝑂 𝐿 20 , and thecross shaped vessel similar Φ and length as the drift pipe.

MEASUREMENTS
Measurements were carried out for hydrogen beams extracted at 5 and 10 kV. Figure 2 shows measured 2D mapsof beam current, 𝐼𝑚 , versus 𝑆𝑂 𝐿1 and 𝑆𝑂 𝐿2 excitation currents, 𝐼𝑆𝑂𝐿1 and 𝐼𝑆𝑂𝐿2 at ACCT2, ACCT3, and ACCT4. 𝐼𝑚
at ACCT3 and ACCT4 presented similar values and patterns
with contributions from different species, due to mass-tocharge ratio and collimation effects.

SIMULATIONSThe General Particle Tracer (GPT) code [6] has designed
the extraction electrode optical system design of ESS Bilbao
injector [7], and was used to simulate single 𝐻 + , 𝐻2+ , and𝐻3+ beams at 5 and 10 kV. Electromagnetic fields for extraction electrodes and LEBT solenoids were calculated with
COMSOL Multiphysics [8]. Simulations were performed
for the same magnetic fields considered for measurements.
Measured beam currents at ACCT1 were nearly constant,and their mean values were used as inputs. For 5 kV beams:
𝐼𝑖−5𝑘𝑉 = 1.1 mA; and for 10 kV: 𝐼𝑖−10𝑘𝑉 = 3.2 mA.
Figure 3 illustrates simulated 2D maps of beam currents,
𝐼𝑠 , at ACCT2, ACCT3, and ACCT4 𝑍 𝑝𝑜𝑠 versus solenoids
current for 5 kV beams. The optimum beam current transmission regions at ACCT2 𝑍 𝑝𝑜𝑠 show vertical belt shapes,
but after 𝐶𝑂 𝐿 20 at ACCT3, and ACCT4 we notice optimumtransmission regions are at weaker fields with hyperbolic
triangular shape, and at stronger fields with a hyperbolic
curved shape, only noticed for 𝐻 + and 𝐻2+ species, since for
𝐻3+ would be out of range.
It was found that 𝑋 𝑍-trajectories for beams extracted at
any field configuration within a hyperbolic triangular region,
for example a 5 kV 𝐻 + beam from Fig. 3(c) being 𝐼𝑆𝑂𝐿1 =45 A and 𝐼𝑆𝑂𝐿2 = 32.5 A presented normal focusing having
one focal point, but within a hyperbolic curved region like at
𝐼𝑆𝑂𝐿1 = 55 A and 𝐼𝑆𝑂𝐿2 = 70 A, the beam was over focusedshowing two focal points. Figures 4(a) and 4(b) illustrates
both cases.
Optimum extraction regions for 𝐻 + , 𝐻2+ , and 𝐻3+ beamsimulated at 10 kV were similar to the 5 kV maps from Fig. 3,
but slightly displaced to stronger field values, due to Lorentz
centripetal forces.

† dfernandez@essbilbao.org

MOPB033
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MC1.1 Beam Dynamics, beam simulations, beam transport32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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UPDATE ON ESS-BILBAO RFQ LINAC
J. L. Muñoz∗ , I. Bustinduy, N. Garmendia, J. Martín, D. Fernández-Cañoto, P. González,A. Conde, A. Zugazaga, A. Kaftoosian, ESS-Bilbao Consortium, Zamudio, Spain
Abstract

Table 1: ESS-Bilbao RFQ Main Characteristics

The ESS-Bilbao RFQ fabrication is completed. The RFQ
will operate at 352.2 MHz and will accelerate a 45 mA proton
beam from 45 keV up to 3.0 MeV. The RFQ is build up of 4
copper segments, for a total length of 3.2 m. Each segment iscomposed of 4 subparts, 2 major and 2 minor vanes, that areassembled together by using bolts, vacuum and RF gaskets,with no brazing used in the procedure. This approach enables
possible corrections in the assembly. The machining of all
the segments has now finished. The RFQ structure has beenassembled and the several tests have been carried out on it. In
this paper we present aspects of the mechanical fabricationof the RFQ, the results of the vacuum tests of the whole
structure, with all the tuners and couplers inserted. The low
power RF measurements, frequency spectrum, quality factor
and tuning operations by bead pull technique. Fabricationand testing of the components (tuners, couplers, pickups) arealso presented. The operation of the RFQ is initially planed
for low duty cycle, simplifying water cooling engineeringand couplers design. The tests at low duty cycle will enable
to define the required facilities for the use of the RFQ at its
nominal power for future steps.

INTRODUCTION
The machining of the ESS-Bilbao Radio Frequency
Quadrupole (RFQ) [1, 2] has been completed. This RFQ
will be part of the proton injector for the ARGITU compact
accelerator-based neutron source [3]. Designed to accelerate protons from 45 keV to 3.0 MeV, the RFQ operates as apulsed linear accelerator (linac) at 352.2 MHz with a duty
cycle of up to 5 %.
To achieve the necessary acceleration and transmission
characteristics, the RFQ must be precisely machined andassembled. The ESS-Bilbao RFQ is composed of four segments, each consisting of four vanes. Unlike traditional
designs, these segments are not brazed together; instead,polymeric vacuum gaskets and RF contact elements are usedin the assembly (as described in [1, 2]) to guarantee vacuum
and electrical and thermal contact. Main characteristics of
the RFQ are summarized in Table 1.
The machining, assembly and characterization of individual segments have finished, and results are presented here.
The assembly of the whole structure is in process.
It is relevant to point out that power couplers have alreadybeen built and have been tested in low and high RF power.
One coupler was attached to the RFQ already in operation
at ISIS-FETS facility and tested with nominal peak power,
for low duty cycle, as already reported in Ref. [4].
∗ jlmunoz@essbilbao.org

MOPB034
112

Parameter

Value

Type
4 vaneParticle
Protons
RF frequency
352.2 MHzIntervane voltage
85 kV (uniform)
Energy45 keV ⟶ 3.0 MeVDesign current
60 mA
Input emittance (rms norm)
0.25 π · mm · mrad
Duty cycle
Up to 10%
Kilpatrick factor
1.85
Number of cells
273
𝑅0
3.44 mm
𝜌/𝑅00.85
Input/Output matcher
16.674 mm / 14 mm
Total length
3.12 m (3.66 𝜆)Number of segments
4 (about 800 mm each)
Method of assembly
Polymeric vacuum gaskets
Plunger tuner ports
16 per segment

RFQ FABRICATION
Segments Machining
Each segment is itself an assembly of four components,
two major vanes and two minor vanes (Fig. 1). Major vanes
include the ports for tuners, couplers and pick-ups, as well as
the vacuum ports. All components incorporate vane coolingchannels that run along the segment. Each component is machined starting from a block of raw material (copper grade
ASTM B248 C10100, ISO Cu-OFE), and subsequently machined in several steps until the final geometry is achieved.
During the fabrication process several metrology controls
are realized in order to verify that there are no deviations
from the plan.

Figure 1: Model view of a segment, showing the minor andmajor vanes, the vacuum and RF seals grooves, as well assome details of the exterior.
MOPB: Monday Poster Session
MC3.5 RFQs

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB035

A CRYOGENIC DIELECTRIC PULSE COMPRESSOR

Abstract
Efforts aimed at developing klystron parameters havemade significant progress in recent years [1]. However, theultimate parameter list of connected pulse compressors(PCs) has been given insufficient attention. We propose todevelop a new high efficiency, high power gain pulse compressor based on the use of a dielectric storage resonator(100% dielectric filling factor) that is operated at a cryogenic temperature (77 K). It is well known that, at cryogenic temperatures, a copper cavity can gain a much higher
Q factor. However, at cryogenic temperatures, the RF loss
tangent of some dielectric materials also decreases substantially (tanδ~10-9 for Sapphire at 10 K). This inspires oureffort to develop dielectric resonators for PCs with an intrinsic quality factor, Q0, that is several orders of magnitude
higher than the Q0 for all metallic resonators at room temperature, and at least twice as high as for cryogenic copper
cavities. In addition, the dielectric storage cavity can makethe PC system more compact and lower their cost. We anticipate improving the parameters of the well-known
SLED-II PCs. We consider both a passive PC (switchedwith a fast change of the klystron’s phase) as well as anactive PC (which requires a fast RF switch).

CRYOGENIC HIGH-Q RESONATORS
Two of the best-known pulse compression systems used
for room temperature RF accelerators are the SLED and
SLED-II PCs (Fig. 1). Both of these use hollow copper
storage resonators (SLED) or delay lines (SLED-II) that
accumulate RF energy from an incident RF pulse [2, 3].
The resonators work in low-loss TE01 or higher order axisymmetric modes. Unlike the SLED PC that has a decaying output pulse, the SLED-II was designed to provide aflattop output RF pulse that is the best shape for feeding
accelerating structures. The compressed pulse arises when
the phase of the incident RF pulse is sharply changed by
180°. These PCs are often called passive PCs because theproperties of the resonators or delay lines are neverchanged. A pair of resonators or delay lines are fed by a 3-dB hybrid coupler that protects the RF source from theundesirable reflection that occurs during the transient process of RF power accumulation. The SLED PC can provide
up to 9× power gain, Pg (ratio of the output pulse power tothe incident pulse power). For maximum power gain, theefficiency (η), defined as the ratio of the energy in the output pulse to the incident energy, is very low. Typically,
SLED works with power gain ~4, in which case the compression ratio, Cr (ratio of incident pulse length to thelength of the compressed pulse) equals 6. The efficiency
in this case can be as high as 67% [2].
____________________________________________† s.kuzikov@euclidtechlabs.com

MOPB: Monday Poster Session
MC4.6 RF power sources and power couplers

Figure 1: SLED-II layout. Tested with 12.065-cm diameterwaveguide, 22.5-m in length (150-ns round-trip RF transittime) [2].
The obtainable parameters for the compression, power
gain, and efficiency depend on the internal losses of the
PC. Obviously, the lower the losses, the higher these parameters will be. To reduce the losses in the storage resonators, one can cool them down. Another idea is to substitute low-loss dielectric waveguides for the copper waveguides that are typically employed. Additional loss reduction can be obtained using dielectric materials at cryogenic
temperature, taking advantage of the fact that, below somethreshold temperature, the losses in all types of dielectrics
go down as the temperature is decreased. Table 1 summarizes the properties of two of the most appealing dielectricmaterials, Magnesia and Sapphire, in X-band at different
temperatures. The data for Magnesia are taken from Refs.
[4, 5]. Sapphire, a particular type of Corundum crystal (another one is Ruby), was well characterized in Refs. [6, 7].
Table 1: Properties of Materials at Cryogenic Temperaturesin X-Band
Material

300 K

77 K

45 K

Magnesia ε=9.64
tanδ=7⋅10-7
Sapphire ε=11.6
tanδ=1⋅10-5

ε=9.64tanδ=1⋅10-7
ε=11.36ε=11.34tanδ=1⋅10-8- tanδ=5⋅10-91⋅10-7
1⋅10-7
Quartzε=4.4-4.6
ε=4.4-4.6
ε=4.4-4.6
tanδ=2⋅10-6- tanδ=2⋅10-6tanδ=1⋅10-4
1⋅10-5
1⋅10-5
Let us consider a rod packed in a quartz envelope (seeFig. 2). Good guiding properties come from the effect of
total internal reflection (TIR). A wave propagating in a dielectric rod (made of Magnesia or Sapphire) with a highrefractive index does not leak into a medium, like vacuum
or quartz, which has a low refractive index. Remarkably,
this configuration does not contain any dielectric-vacuum
interfaces at a field level that can cause multipactor discharge.
MOPB035
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S. V. Kuzikov†, Euclid Techlabs LLC, Bolingbrook, IL

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISSN: 2226-0366

doi: 10.18429/JACoW-LINAC2024-MOPB036

ACCELERATING STRUCTURESFOR THE FCC-ee PRE-INJECTOR COMPLEX:
RF DESIGN, OPTIMIZATION, AND PERFORMANCE ANALYSIS
A. Kurtulus, A. Grudiev, A. Latina, CERN, Geneva, Switzerland
S. Bettoni, P. Craievich, J.-Y. Raguin, Paul Scherrer Institut, Villigen, Switzerland
Abstract
The Future Circular Collider electron-positron (FCC-ee)
pre-injector complex demands high-performance RF accelerating structures to achieve reliable and efficient accelerationof beams up to 20 GeV. In this study, we describe an analytical approach to RF design for the traveling-wave (TW)structures including a pulse compression system to meetthe rigorous specifications of the FCC-ee pre-injector complex. The fundamental mode at 2.8 GHz and Higher Order
Mode (HOM) characteristics were determined through theutilization of lookup tables and analytical formulas, enabling
efficient exploration of extensive parameter ranges. Optimization of the structure geometry and in particular theiris parameters was performed to address key challenges including maximizing effective shunt impedance, minimizing
surface fields, and effectively damping long-range wakes
through HOM detuning. Moreover, we investigated the impact of beam-loading effects on the bunch-to-bunch energy
spread. Comprehensive thermal and mechanical analyses
were carried out to evaluate the impact on the accelerating structure performance during operation at a repetition
frequency of 100 Hz.

INTRODUCTION

The proposed new baseline for the FCC-ee injector complex [1] includes an updated high-energy linear accelerator(HE linac). This design enhancement increases the numberof bunches per RF pulse from two to four while reducing therepetition rate to 100 Hz. Each bunch will have a charge of
5 nC, an rms length of 1 mm, and a bunch spacing of 25 ns.
The following section provides an update on the RF design, optimization, and performance analysis, including themethodology and specific structural features of the HE linac.

RF DESIGN METHODOLOGY
A parametric study was conducted to optimize accelerator
structure design. Lookup tables were generated to rapidly
assess the impact of aperture radius a and iris thickness d on
the first twenty HOMs of a convex cell at the synchronous
frequencies. The primary design goal was to enhance shunt
impedance relative to previous S-band structures [2]. The
target structure was defined by an RF frequency of 2.8 GHz,
RF phase advance 𝜓 of 120° per cell, and a length 𝐿𝑠 of
3 meters. An average aperture of 0.12𝜆 [3] (equivalent to12.85 mm) was selected as a suitable compromise between
beam dynamics and RF considerations. The long-range
transverse wake is damped through the detuning of dipole
modes, eliminating the necessity for additional damping
MOPB: Monday Poster Session
MC2.2 Electron linac projects

elements. This is accomplished by tapering the apertureand iris thickness while maintaining an average aperture of
0.12𝜆. The design constraint requires that the transverse
wakefield potential 𝑊𝑡 remains at or below 0.1 V/pC/mm/m
within the time range of 25 to 100 ns.
A SLED-type [4] RF pulse compressor was analyticallydesigned and implemented to further optimize the performance. This device increases the peak amplitude of the
RF pulses and shortens their duration by storing energy
in a cavity and then releasing it in a compressed form.
The resultant boost in peak RF power significantly impacts the electric field strength within the accelerator cavities, which is essential for achieving the target acceleration gradients. Consequently, the effective shunt impedance𝑅eff = ⟨𝐺(𝑡 = 𝑇𝑘 )⟩2 𝐿𝑠 /𝑃𝑘 (where ⟨𝐺(𝑡 = 𝑇𝑘 )⟩ is the average
gradient at beam injection, 𝐿𝑠 is the length of the structure,and 𝑃𝑘 is the klystron power), which measures the efficiencyof RF power transfer to the beam, was carefully evaluated.

OPTIMIZATION OF THE RF STRUCTURE
A parametric sweep was conducted to optimize the HE
linac RF structure design based on shunt impedance calculations. Using a lookup table, iris thicknesses ranging
from 2.04 mm to 6.2 mm were tested to maximize shunt
impedance.
To assess tapering effects, the delta Δ parameter was introduced as an offset relative to the constant aperture structure,adjusting the first and last cell apertures while maintaining
a linear variation between them. Positive delta values resulted in down-tapering (larger first cell aperture, smaller
last cell), and negative values led to up-tapering. Delta wasvaried from -4 mm to 4 mm in 0.2 mm steps, and the highest
shunt impedance was identified. Finally, a wakefield analysis was conducted using frequency-domain parameters of 20
lowest HOMs, with designs selected based on analyticallycalculated wakefields that remain below 0.1 V/pC/mm/m,
refining the linac’s aperture and iris thickness for optimal
performance.
Figure 1 presents the results of a parametric sweep of maximum effective shunt impedance as a function of the delta parameter. The red traces depict the effective shunt impedancevalues under conditions where transverse wakefields are notconstrained, providing a baseline for comparison. In contrast, the blue traces illustrate the effective shunt impedance
when the transverse wakefield is limited to a threshold of
0.1 V/pC/mm/m. We observed that a delta of 2 mm achieves
the highest effective shunt impedance while meeting wakefield constraints and exhibiting a low surface electric field
MOPB036
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ISBN: 978-3-95450-219-6

JACoW Publishing32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB038

A. Malyzhenkov∗ , A. Aksoy, R. Corsini, W. Farabolini, A. Gilardi, A. Latina, P. Korysko1
CERN, Geneva, Switzerland
1 also at University of Oxford, Oxford, United Kingdom
Abstract
Corrugated structures have recently been utilized for thetime-resolved diagnostics of electron bunches and freeelectron-laser (FEL) pulses across several FEL facilities:
SwissFEL at PSI and European XFEL at DESY. Thisapproach is simple and cost-effective, based on the selfstreaking of electrons with a transverse wakefield enhanced
in such structures. In this work, we optimize the design ofa corrugated streaker for the wide range of beam parameters of the CERN Linear Electron Accelerator for Research(CLEAR). We report on the fabrication of corrugated plateswith various corrugation parameters and their initial installation for in-air measurements at CLEAR. Variable polarization streaking can be achieved either by mechanicallyrotating the plates or by utilizing two pairs of corrugatedstreakers. Additionally, we emphasize that when streaking
in the vertical (or horizontal) direction with one structure,
the undesired quadrupole wakefield can be compensated by
the second orthogonally oriented streaker. This allows for asignificant improvement in the resolution of the method.

INTRODUCTION
CLEAR is a user facility providing an electron beam witha wide range of parameters for user experiments, summarized in Table 1 [1–4]. The layout of the CLEAR beamline
is shown in Fig. 1 featuring several Test Areas for the experiments. Characterization and control of the bunch length,
temporal profile distribution, and longitudinal phase spaceof the electron bunch are of great importance for several user
experiments. Currently, such diagnostics are realized by utilizing an S-band transverse deflector driven by a dedicatedklystron. The transverse deflector has a footprint of around
20 cm, excluding the waveguides, and provides a temporal resolution of ∼100 fs for 200 MeV electron beams whenmeasuring the streaked beam at the MTV390 screen [5].
All test areas are located downstream of the transverse
deflector and the first measurement screen. Therefore, noninvasive shot-to-shot online diagnostics of the bunch length
are currently not available at CLEAR, although experiments
could benefit from such capabilities. Moreover, temporal
diagnostics may be of significant interest for monitoring
beam properties in the second beamline planned to be implemented at CLEAR, using the bending magnet BHB0400
to direct the beam in the opposite direction from the Vesper
Test Area. In this work, we explore a cost-effective and elegant approach of employing a corrugated passive streaker for

Table 1: CLEAR Beam Parameters
Parameter
Bunch charge
Bunch length RMS
Beam Energy
Beam Energy Spread
Bunch frequency
Norm. emittanceBunches per pulse
Max. pulse charge
Repetition rate

Value
0.005 − 1.6 nC
0.1 − 10 ps
30 − 220 MeV< 0.2% rms (< 1 MeV FWHM)
1.5 or 3.0 GHz
1 − 20 µm
1 − 150∼90 nC0.8333 − 10 Hz

temporal diagnostics, which was successfully implemented
at SwissFEL [6] and EXFEL [7].

SIMULATION RESULTS
Each corrugated streaker installed at SwissFEL is approximately 1 m long, consisting of two pairs of corrugatedstreakers attached to micron-precision moving motors, withthe entire setup integrated into a vacuum chamber [6,8]. The
approximate cost of a single unit is around 110 kCHF, which
is roughly an order of magnitude less than that of an active
C-band or X-band deflecting cavity with a power supply [6].
However, even this amount is still a significant investment
for a single diagnostic system in a small medical accelerator
or an electron linac at an irradiation facility such as CLEAR.
In comparison to the 6 GeV beam energy at SwissFEL, themaximum beam energy at CLEAR is limited to 200 MeV.
For this energy, and considering that the shortest bunch
length at CLEAR is approximately 100 fs, we optimized thedesign of the corrugated plates to minimize production costand footprint. Another characteristic worth comparing is
the active S-band deflector installed at CLEAR, which isapproximately 20 cm long, excluding the waveguides andpower supply system. We performed a series of numerical simulations assuming a corrugated plate length of only
10 cm and validated that the streaking effect, even for the
shortest bunches at CLEAR, is well-pronounced and would
enable reconstruction of the temporal profile of the electron
bunch with a resolution similar to that of the active S-band
deflector.
Figure 2 shows the results of numerical simulations at
a measurement screen placed 0.5 m downstream from thecorrugated streaker. In these simulations, we use the analytical model from [9] for plates with 500 µm corrugation,∗ alexander.malyzhenkov@cern.ch

MOPB: Monday Poster Session
MC4.1 Beam diagnostics

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VARIABLE POLARIZATION SELF-LOCKED STREAKING OF
ELECTRONS IN TIME WITH A PAIR OF CORRUGATED STRUCTURES

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB039

A. Latina, CERN, Geneva, Switzerland
Abstract
In high-intensity linacs, bunch-to-bunch effects due to theexcitation of short and long-range wakefields can lead tobeam instabilities and beam breakup. Wakefields can be due
to resistive or geometric effects excited in the RF structures
or in the beam pipe. From version 2.3.0 onwards, the particle
tracking code RF-Track has been modified to implement a
multi-bunch beam model that simplifies and optimises thecalculation of single and multi-bunch effects. The effect of
wakefields on the beam is assessed by computing the action
amplification due to incoming jitter. The jitter amplification due to multi-bunch effects is evaluated using a 1 GeVelectron linac example.

INTRODUCTION
Linacs for high-energy physics colliders, medical applications, compact X-ray sources, such as Inverse Compton Scattering sources, and compact accelerator-based neutron production require high-intensity beams. When high-intensity
beams are injected into linacs, intensity-dependent effects
such as beam loading and short- and long-range wakefields
in the accelerating structures must be considered. The effectof beam loading is primarily to reduce the effective accelerating gradient available in the RF structures as high-charge
bunches travel through them. The effect of wakefields degrades the beam quality by causing transverse deflections,energy loss, emittance growth, energy spread increase andultimately, beam breakup. In this paper, we focus on evaluating the effect of wakefields on beam jitter, both in single
and multi-bunch operation, using the CERN tracking code
RF-Track [1]. This code can also simulate the effects ofbeam loading, as presented in Ref. [2].

RF-Track v2.3.0
Initially developed for the design and optimisation of a
medical proton and light ion linac [3], RF-Track has evolved
over the years to extend its simulation reach and range ofapplications, becoming the primary design tool for many
projects and studies: e.g., the “Deep Electron FLASH Therapy” (DEFT) facility [4], the positron sources of SuperKEKB [5], the CLIC and FCC-ee injector linacs [6, 7], Inverse
Compton scattering sources [8], and the cooling channel ofa future muon collider [9].
Up to version 2.3.0, RF-Track could only simulate single
bunches. It was still possible to simulate bunch-to-bunch
long-range effects using the standard trick of creating a single “super bunch” with all individual bunches suitably separated in time. This workaround, while working in somecases, introduced several inconveniences: it complicated thepost-processing of the output data to separate the individual
MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transportbunches; it undermined the simulation of single-bunch effects such as short-range wakefields or space-charge, whosealgorithms are designed to operate in the short-range regime.
In version 2.3.0, the tracking core of RF-Track has beenrewritten to handle multi-bunch beams rather than single
bunches, introducing the new object Beam. In RF-Track, a“Beam” is a set of single bunches that the user can specify
individually at arbitrary distances from each other. The main
innovation and benefit of the new object is that it allows a
specialised implementation of long-range collective effects
for multi-bunch beams. For example, specific single-bunch
effects such as space charge are applied to each bunch individually, while bunch-to-bunch effects such as long-range
wakefields can be computed considering the large spacing
between bunches using a dedicated long-range algorithm.
In addition, accessing information about each bunch andanalysing the results after tracking is now much easier. The
new “Beam” model also increases flexibility, for example,
by allowing the user to simulate bunch trains where somebunches are single particles while others are multi-particles,
thus speeding up simulations where one needs to focus ona specific bunch. Moreover, the bunches can be arbitrarily
and irregularly spaced, have different charges and even beof different species.
It should be noted that these changes have been implemented to maintain backward compatibility with older simulation scripts, so when the user is working with single
bunches, RF-Track behaves in the same way as in previous
versions.

Example of Beam Definition
The following lines provide an example declaration of a
train consisting of 30 equally spaced bunches:% Define a bunch
bunch = Bunch6d(mass, charge, q, phase_space);% Define the train structure
num_of_bunches = 30; % train length
bunch_spacing = 1/3 * ns; % bunch spacing% Define a beam
B0 = Beam(bunch, bunch_spacing, num_of_bunches);

If “LINAC” is an arbitrary beamline, then B1 =LINAC.track(B0); is the outcoming train, whereB1{1} is the first bunch, B1{2} is the second, etc.

JITTER AMPLIFICATION
Single-bunch Short-range Wakefields
A detailed explanation of the Wakefield models implemented in RF-Track was presented in Ref. [10]. The effect ofshort-range wakefields on a bunch, in addition to introducing
correlated energy spread and slice emittance growth, is also
MOPB039
127

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STUDIES OF SINGLE AND MULTI-BUNCH INSTABILITIES IN LINACSUSING RF-TRACK

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB041

J. Olivares Herrador∗ 1,2 , A. Latina1 , N. Fuster-Martinez2 , B. Gimeno2 , D. Esperante2,3
1
CERN, Geneva, Switzerland
2
Instituto de Física Corpuscular (IFIC); CSIC-University of Valencia, Paterna, Spain
3
Department of Electronic Engineering—ETSE, University of Valencia, Burjassot, Spain
Abstract
High intensity linacs based on compact accelerating RF
structures suffer from beam loading effects, which result into
a bunch-to-bunch energy loss as a consequence of the beaminduced excitation of the fundamental accelerating mode. To
track charged particles under this effect, the code RF-Track
implemented a beam loading module in version 2.2.2. For
ultrarelativistic scenarios in travelling-wave structures, thesimulation tool was limited to trains of bunches with equalcharge per bunch. In this work, we present the latest updateof the beam loading module in version 2.3.0, extending its
capabilities to account for this effect in trains with different
charges per bunch and allowing the performance of beamloading compensation studies in these scenarios.

INTRODUCTION𝑟𝑟
𝜕𝐺𝜕𝐺 ⎛ 𝜕𝑣𝑔 𝑣𝑔 𝜕 𝑄 𝜔 ⎞ 𝐺 𝜔 𝑄 𝒯𝐼 ̃
−
= 𝑣𝑔
+⎜
− 𝑟
+ ⎟ +
, (1)
𝜕𝑡
𝜕𝑧 ⎝ 𝜕𝑧
𝜕𝑧
𝑄⎠ 2
2
𝑄

where 𝐺 is the gradient, 𝜔 the angular frequency, 𝑣𝑔 thegroup velocity of the cavity, 𝑄 its unloaded quality factor,
𝑟/𝑄 the normalized shunt impedance per unit length, 𝒯 thetime-transit factor and 𝐼 ̃ is defined as:(2)

with 𝐹 being the form-factor of the bunch, 𝑞bunch its total
charge, 𝛽𝑧 its average longitudinal velocity (normalized by
the speed of light 𝑐) and 𝑇 the RF period.
∗ javier.olivares.herrador@cern.ch

MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

FLEXIBLE BEAM LOADING MODEL
The longitudinal electric field (𝐸𝑧 ) of the fundamental
mode of a lossless TW structure can be written, by means of
the Floquet theorem, as the superposition of several spatial
harmonics (𝑙 ∈ ℤ) as:∞

The Beam Loading (BL) effect is the gradient reductionthat occurs in accelerating radiofrequency (RF) structures,
when the particles traveling through it excite the fundamental mode, which exhibits a decelerating longitudinal electricfield. Energy conservation requires that bunches lose energy in order to excite the mentioned mode [1]. In addition,
given that standard operation discourages the damping of
the fundamental mode, each bunch-induced excitation will
last in the cavity for a long time. For this reason, consecutive
bunches can also lose energy when they are affected by thebeam induced field left by earlier ones.
A self-consistent module to simulate BL effects upon
particle tracking was implemented in RF-Track’s version
2.2.2 [2]. It is based on the power-diffusive model derived
in Ref [3], which, for travelling-wave (TW) structures, gives
the following gradient reduction equation:𝑞𝐼 ̃ = 𝛽𝑧 bunch 𝐹,
𝑇

Version 2.2.2 calculated beam loading effects based on
the resolution of Eq. (1) prior to tracking, as bunches withequal charge and velocity 𝑐 were assumed. This limits thesimulation of scenarios where particles are lost along theaccelerator, or where trains with different charge per bunch
are injected. For this reason, a more flexible algorithm has
been implemented in version 2.3.0, whose major upgrades
are presented in this conference proceedings at [4].

𝐸𝑧 (𝑧, 𝑡) = Re [ ∑ 𝐸𝑙 exp (−𝑗(𝑘𝑙 𝑧 + 𝜔𝑡)] ,

(3)

𝑙=−∞

where 𝑗 is the imaginary unit, 𝐸𝑙 ∈ ℝ is the amplitude ofeach harmonic and 𝑘𝑙 its wave number, which satisfies thefollowing property:
2𝜋.
(4)𝑘𝑙 − 𝑘𝑙−1 =𝐿where 𝐿 stands for length of each periodic cell.
Usually, TW structures are designed in a way that thephase velocity of one harmonic, 𝑙∗ , is 𝑐 and 𝑘𝑙∗ = 𝜔/𝑐. In
this case, for an ultrarelativistic particle, the gradient reads
as:
𝑧
1 𝐿
𝐺(𝑧) = ∫ d𝑧𝐸𝑧 (𝑧, ) =𝐿 0𝑐𝐿2𝜋(𝑙 − 𝑙∗ )𝑧
1 +∞= ∑ 𝐸𝑙 ∫ cos () d𝑧
0
𝐿 𝑙=−∞
𝐿+∞= ∑ 𝐸𝑙 [𝑙=−∞sin (2𝜋(𝑙 − 𝑙∗ ))] = 𝐸𝑙 ∗ .
2𝜋(𝑙 − 𝑙∗ )(5)Equation (5) provides a physical meaning to the accelerating gradient: It is the amplitude of the spatial harmonic
whose phase velocity synchronizes with the beam velocity.
Therefore, solving Eq. (1) for a single particle (𝐺single ),one can compute the longitudinal electric field excited by thisparticle as 𝐸𝑧 (𝑧, 𝑡) = Re [𝐺single (𝑧, 𝑡) exp (−𝑗𝜔(𝑧/𝑐 − 𝑡))].
With this, the longitudinal wakefield (𝑤𝑙 ) caused by thisparticle upon a test particle located at a distance 𝑠 can be
defined as [5]:∞𝑐𝑤𝑙 (𝑠) =∫ d𝑡𝐸𝑧 (𝑐𝑡 − 𝑠, 𝑡) .
(6)
𝑞single −∞MOPB041
131

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BEAM LOADING COMPENSATION IN CHARGE-VARYINGSCENARIOS WITH RF-TRACK

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB042

A. Mamaras†1, M. Koopmans, J. B. Lallement, A. M. Lombardi, F. di Lorenzo, E. Pasino,
D. Sampsonidis1, CERN Geneva, Switzerland
1
also at AUTh, Thessaloniki, Greece
Abstract
As part of CERN's medical application research, a compact electrode system (< 30 cm) has been designed to facilitate low-current, multiparticle beam extraction andmatching to a high-frequency RFQ. This study explores theinnovative extraction system design and evaluates its simulation performance. Superfish (SF) and CST Studio Suite
were employed to export the 2D and 3D electric field mapsof the extraction system for beam dynamics simulations.
Beam dynamics simulations using the Travel code haveconfirmed the system's ability to deliver a high-quality,
low-current particle beam fully matched to a 750 MHz
RFQ, capable of accelerating particles with a 𝑞/𝑚 ratio of½ to 1. This paper provides an overview of the key design
considerations, geometry layout, and beam dynamics results.

INTRODUCTION
Hadron therapy is a well-established and effective treatment method for severe cancer cases [1]. In hospital environments, the typical accelerator complex used for hadron
therapy comprises a linac pre-injector and a synchrotronthat delivers the beam to treatment rooms. Standard linac
pre-injectors include an ion source with its extraction system, a Low Energy Beam Transport Line (LEBT), and aRadiofrequency Quadrupole (RFQ), which accelerate andtransport the beam to the next accelerating structure.
The need for sustainability and high daily performancehas driven research towards designing a more compact andefficient accelerator facility. This approach aims to reduce
the required space and power consumption while ensuring
a high-performance, reliable, and user-friendly machine.
At CERN in the framework of NIMMS a new compact extraction system has been developed to provide a multiparticle beam directly to the RFQ, eliminating the need for a
LEBT and efficiently meeting low-current injection requirements.

DESIGN METHODOLOGY
The extraction system is envisioned to integrate into an
experimental setup comprising a commercial RF ion
source from National Electrostatics Corp. (NEC) [2] and a
two-cavity RFQ operating at 750 MHz. This RFQ is capable of accelerating ions with a charge-to-mass ratio (𝑞/𝑚)of ½ to 1, e. g. 12C6+, 4He2+ or H+, for hadron therapy [3].
Therefore, the new extraction system must be specificallydesigned not only to accelerate the beam to the desired energy of the RFQ but also to focus and match the beam with
the Twiss parameters required by the first RFQ cavity's† aristeidis.mamaras@cern.ch
MOPB: Monday Poster Session
MC3.1 Industrial and medical accelerators

matching plane (MP), as detailed in Table 1. The RFQ MP
is a critical reference plane at the entrance of the first RFQ
cavity, where the beam parameters must be precisely
matched to ensure optimal beam transmission (total acceptance) and acceleration.
Table 1: Transverse Acceptance Parameters of the First
RFQ Cavity
Twiss Parameters

X planeY plane

Alpha
0.26
0.32
0.01
0.01
Beta / 𝑚𝑚/𝑚𝑟𝑎𝑑
~0.80
~0.79
Total Acc. Norm / 𝑚𝑚 ∙ 𝑚𝑟𝑎𝑑
The extraction system consists of a fixed-shaped source
electrode mounted on the plasma chamber, a puller electrode, and two additional electrodes to ensure versatility
and adaptability to a wide range of particle types and energies while adjusting the matching to the input plane of thefirst RFQ cavity. The nominal energy provided by the extraction system is 15 keV/u, set by the input energy accepted by the first RFQ cavity with the extracted current
ranging up to several μA. Given that the source initiallyprovides a probe extraction energy of 1 keV, the remaining
potential difference for extraction is 14 kV. The electrodes
are metallic hollow discs with apertures sized to be at least
1.5 times the total transverse beam size in both planes, preventing electrode damage from potential beam loss.
These losses may result from possible misalignments inthe extraction system or the divergence of the extracted
beam. To address this, the electrodes have been designedwith a thickness of 5 mm, capable of withstanding current
losses up to tens of μA. To determine the optimal design
configuration that meets the characteristics of the RFQ MP
listed in Tables 1 and 2, a minimization algorithm incorporating the model of aperture lenses was developed [4].
Table 2: Key Characteristics and Optimized Parameters of
the Extraction System
System Characteristics
Electrodes Thickness / mm
5Particle beam energy / keV/u
15
Probe voltage / kV
1
Total potential difference / kV
14
Total system length, dtot / cm
< 30
Drift length, ddrift / cm
10
Optimised params
V1,2, d1,2,3, r1,2,3
The algorithm defined the optimal combination of potential V1,2 and distances d1,2 of the two additional electrodes, as seen in Fig. 1, following a mismatch function that
MOPB042135

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DIRECT INJECTION EXTRACTION SYSTEM INTO A HIGH FREQUENCYRADIOFREQUENCY QUADRUPOLE FOR MEDICAL APPLICATIONS

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB043

L. M. Wroe, A. Latina, S. Stapnes, W. Wuensch, CERN, Geneva, Switzerland
R. J. Apsimon1 , M. Southerby1 , Lancaster University, Lancaster, United Kingdom1
also at Cockcroft Institute, Warrington, United Kingdom
Abstract
In this paper, we derive the multipolar form of thechange in transverse and longitudinal momenta of an ultrarelativistic charged particle that traverses a harmonic TM𝑚𝑛0
mode in a pillbox cavity with a beam pipe. The relevant
equations are first formalised before presenting results fromthe numerical integration of RF cavity field maps. In particular, we show that the radial dependence of the change
in transverse and longitudinal momenta through a TM𝑚𝑛0
mode has polynomial, and not Bessel, dependence.

INTRODUCTION
In 1956, Panofsky and Wenzel derived their eponymoustheorem stating that the change in transverse momentumΔ𝑝⟂ of a rigid particle of charge 𝑒 and ultra-relativistic velocity 𝑣 ⃗ = 𝑐𝑧 ̂ which traverses an RF cavity supporting amode 𝑙 of resonant angular frequency 𝜔𝑙 and longitudinal
electric field 𝐸𝑧 is [1, 2]
Δ𝑝⟂ (𝑟, 𝜃) = −𝑖𝑒 𝐿/2∫
∇ 𝐸 (𝑟,⃗ 𝑡)𝑑𝑧.
𝜔𝑙 −𝐿/2 ⟂ 𝑧

𝑒 ∞ 𝑖(𝜔𝑙𝑧/𝑐+𝜓)∫ 𝑒∇⟂ 𝐸𝑧 (𝑟)𝑑𝑧.
⃗
𝜔𝑙 −∞

(2)

∞

−∞

𝑑𝑘

𝑘 < 𝑘𝑙 ;otherwise,(4)

where 𝜅2𝑙 = |𝑘 2 − 𝑘𝑙2 | and 𝑘𝑙 = 𝜔𝑙 /𝑐 is the wavenumber ofthe mode.
In this representation, 𝑔𝑚
̃ (𝑘) has no dependence on radius.
Therefore, if the longitudinal field 𝐸𝑧 is completely known on
the surface of a cylinder of radius 𝑎, 𝑔𝑚 (𝑘) can be explicitly
calculated as𝑔𝑚̃ (𝑘) =∞ 𝑑𝑧
1∫𝑒−𝑖𝑘𝑧 𝐸𝑧,𝑚 (𝑎, 𝑧).
𝑅𝑚 (𝜅𝑙 𝑎) −∞ √2𝜋(5)

By solving Eq. 5, the longitudinal electric field is then also
calculable at any point in the cavity using Eq. 3 and, from this,so too is the change in transverse momentum by PanofskyWenzel’s Eq. 2 which becomesΔ𝑝⟂ = −𝑖Thus the change in transverse momentum is simple to calculate if the longitudinal electric field is known completely.
A completely general representation of the spatial component of the longitudinal electric field for a standing-wave
mode 𝑙 in an RF cavity is derived in Ref. [3] as𝐸𝑧 (𝑟)⃗ = ∫⎧{𝐽 (𝜅 𝑟),𝑅𝑚 (𝜅𝑙 𝑟) = ⎨ 𝑚 𝑙{⎩𝐼𝑚 (𝜅𝑙 𝑟),(1)

Here 𝐿 is a longitudinal length that is sufficiently longer
than the RF cavity such that electromagnetic fields decay
to a negligeble value, 𝐸𝑧 (𝑟, 𝜃, |𝑧| > 𝐿) ∼ 0, and the integral
limits in Eq. 1 can be replaced with 𝐿 → ∞.
In the case of the ultra-relativistic particle having coordinate 𝑧 = 0 at 𝑡 = 0 such that 𝑡 = 𝑧/𝑐 and the harmonic RF cavity mode having phase 𝜓 at 𝑡 = 0 such that𝐸𝑧 (𝑟,⃗ 𝑡) = 𝐸𝑧 (𝑟)𝑒
⃗ 𝑖(𝜔𝑙𝑡+𝜓) , Panofsky-Wenzel’s Eq. 1 becomesΔ𝑝⟂ (𝑟, 𝜃) = −𝑖

is normal and 𝜙𝑚 = 𝜋/2 skew). Furthermore,

∞ 𝑑𝑘
𝑒 ∞
∫ ∇⟂ ( ∫𝑒𝑖𝑘𝑧 𝑒𝑖(𝑘𝑙𝑧+𝜓)
−∞
−∞
𝜔𝑙
√2𝜋
∞

∑ 𝑔𝑚
̃ (𝑘)𝑅𝑚 (𝜅𝑙 𝑟) cos (𝑚𝜃 − 𝜙𝑚 ))𝑑𝑧. (6)𝑚=0From here, we present analytical and numerical resultsfrom field map integrations using Mathematica [4] to derive the form of the change in transverse momentum throughTM𝑚𝑛0 modes in RF cavities.

PILLBOX CAVITIES WITH BEAM PIPES
Figure 1 shows a pillbox cavity with a beam pipe andthe relevant parameters used for this analysis: 𝐺 is the cell
length, 𝑅 the cavity radius, 𝑎 the beam pipe radius, and 𝐿
the field map length.

𝑒𝑖𝑘𝑧 ∞∑ 𝑔𝑚
̃ (𝑘)𝑅𝑚 (𝜅𝑙 𝑟) cos (𝑚𝜃 − 𝜙𝑚 )√2𝜋 𝑚=0∞= ∑ 𝐸𝑧,𝑚 (𝑟, 𝑧) cos (𝑚𝜃 − 𝜙𝑚 ). (3)𝑚=0In this formalism, 𝑔𝑚
̃ (𝑘) has the same units as the electricfield and represents the strength of the multipole of order 𝑚and 𝜙𝑚 is the orientation of the multipole of order 𝑚 (𝜙𝑚 = 0
MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

Figure 1: Cross-section of a pillbox cavity with beam pipe.
MOPB043
139

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ANALYSIS OF THE PANOFSKY-WENZEL THEOREM
IN PILLBOX CAVITIES WITH A BEAM PIPE

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISSN: 2226-0366

doi: 10.18429/JACoW-LINAC2024-MOPB045

DESIGN OF A HELIUM ION LINEAR ACCELERATOR FOR INJECTION
IN A PARTICLE THERAPY SYNCHROTRON AND PARALLEL PRODUCTION OF RADIOISOTOPES*
L. Nikitovic1, 2, †, T. Torims2 and M. Vretenar1
1
European Organization for Nuclear Research (CERN), Geneva, Switzerland
2
Riga Technical University (RTU), Riga, Latvia
Abstract
Interest in helium ions for cancer therapy is growing,
motivated by their superior conformality as compared toprotons or carbon. Clinical trials are starting, using beams
produced by large carbon synchrotrons. To exploit the potential of this new ion, a compact synchrotron is being designed to accelerate helium and protons at treatment energies, for about half the size of a carbon machine. The helium linac is designed to operate at a higher duty cycle thanthe one required for synchrotron injection. Beam pulses
can be sent to target-producing radioisotopes, in particularalpha emitters to be used for targeted alpha therapy of cancer.
The 352 MHz linac is made of 3 sections. To increase
the efficiency with respect to a standard Drift Tube Linac(DTL), the first section from 1 to 5 MeV/u is made of a
Quasi-Alvarez DTL, a structure combining high efficiency
and smooth beam optics. Only this section is powered
when injecting helium ions into the synchrotron. The second and third sections of the DTL type have energies of 7.1
MeV/u, the threshold for the production of 211At, the mostwidely used alpha emitter, and 10 MeV/u, for the production of other radioisotopes.

accelerating tanks and dimensioning cooling system andpower supplies for operation at higher duty cycle can provide with minor investment an effective system for radioisotope production. Operation at 50 Hz repetition frequency
with pulse length of 2 ms (10 % duty cycle) can provide
enough radioisotope doses as required by a medium-size
hospital [5]. One linac pulse out of 50 will go to the synchrotron that operates at 1Hz repetition frequency.
The layout of the complete facility for helium ion therapy and production of radioisotopes is presented in Fig. 1[4]. After the linac, a magnet allows choosing the beam
destination between the radioisotope production target andthe synchrotron.

INTRODUCTION
Helium ions can be effectively used for production ofseveral radioisotope species of medical interest, in particular those used for Targeted Alpha Therapy (TAT). This
technique involves linking alpha-emitting radioisotopes toa carrier that is injected and absorbed by cancerous cells,
thus delivering an intense and localized radiation dose. Investigations of the usage of TAT on tumors such as prostatecancer, neuroendocrine tumors, or brain cancers are progressing, with several ongoing clinical trials [1].
In parallel, there is a renewed interest in directly using
helium ions for cancer treatment, related to their better conformality compared to protons or carbon ions [2]. Treatment of deep-seated tumors at beam energy of 250 MeV/u
can be realized after acceleration in a compact synchrotronof the He2+ beam provided by a linac injector [3, 4].
To satisfy both requirements above, the design of a linear
accelerator that can inject helium ions into a therapy synchrotron and produce in parallel a wide range of therapeutic radioisotopes is presented in this paper. Modifying thesynchrotron injector linac with the addition of two---------------------------------------------------------------------* This study was partially supported by the European Union H2020 research and innovation programme under GA 101008548 (HITRIplus).
† lazar.nikitovic@cern.ch
MOPB: Monday Poster Session
MC3.1 Industrial and medical accelerators

Figure 1: Layout of compact cancer therapy facility [4].

LINAC DESIGN
The linac as synchrotron injector must deliver 5 mA of
He2+ ions at the energy of 5 MeV/u, as required for multiturn injection [4]. For production of 211At, the most promising alpha emitter for TAT [6], the linac has to provide an
additional acceleration up to 7.1 MeV/u. An additional section to 10 MeV/u allows production of other radioisotopes
like 47Sc, 67Cu and 123I [7-9].
The proposed linac is made of three cavities, all at
352 MHz frequency. The first structure is a Quasi-Alvarez
Drift Tube Linac (QA-DTL) [10]. This structure has been
selected since it presents a higher shunt impedance compared to a conventional DTL, and for light ions has comparable shunt impedance to IH-DTL structures withcleaner beam optics [11]. The QA-DTL is followed by two
MOPB045
143

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ISBN: 978-3-95450-219-6

JACoW Publishing32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB046

Elena Donegani∗,1 , Vincent Bertrand2 , Ibon Bustinduy3 , Viatcheslav Grishin1 , Tara Hodgetts4 ,Carlos Neto1 , Anders Olsson1 , Laurence Page1 , Marcos Ruelas4 , Tom Shea1
1 European Spallation Source (ESS) Lund, Sweden
2 Pantechnik, Bayeux, France
3 ESS Bilbao, Zamudio, Spain
4 RadiaBeam Technologies, Santa Monica, CA, USA
Abstract
The commissioning of the Normal Conducting Linac(NCL) of the European Spallation Source (ESS) in Lund
(Sweden), started in September 2018 and was completed inJuly 2023. The four NCL commissioning phases required
the design, procurement, test, installation and operation offour distinct beam destinations in order to safely dump the
proton beam and measure the current of protons with energyof 75 keV in the LEBT, 3.6 MeV in the MEBT, 21 MeV in
the DTL1, and up to 74 MeV in the DTL4.
Each beam destination was operated under UHV, and designed to be as compact as possible while withstanding theFast Tuning mode (62.5 mA, 5 μs, 14 Hz), and the Slow
Tuning mode (62.5 mA, 50 μs, 1 Hz). The EPICS-based
control system was fundamental for five main reasons: (1)the control of the motion in and out of the beam line, (2)the high voltage control in the [0, -1000 V] range, (3) themonitoring of the water cooling systems, (4) the proton current measurements and (5) the timing synchronization withthe overall ESS NCL. Key milestones and measurements
results are described to demonstrate the proton transport
at the nominal current of 62.5 mA during each of the fourcommissioning phases.

THE ESS NCL COMMISSIONING:HISTORICAL BRIEFING FROM THE
POINT OF VIEW OF THE BEAM
DESTINATIONSThe European Spallation Source (ESS [1]) is located in
Lund (Sweden) and it will be a 5 MW pulsed neutron source
once 2 GeV protons will be accelerated onto the ESS tungsten target. Once fully commissioned, the ESS proton accelerator will produce 2.86 ms long protons pulses at a repetition rate of 14 Hz. The nominal proton current of the ESS
accelerator is 62.5 mA. The commissioning of the ESS Normal Conducting Linac (NCL) was completed in four stages
between 9/2018 and 7/2023 (see Fig. 1). Correspondingly,
four beam destinations (namely LEBT, MEBT, DTL1 andDTL4 FC i.e., Faraday cups) were workhorses to safely dissipate the beam power and measure the proton current as wellas the pulse length (see Table 1). The beam destinations weremore compact and less expansive with respect to the usually∗ elena.donegani@ess.eu

MOPB: Monday Poster Session
MC4.1 Beam diagnostics

Figure 1: The four phases of the commissioning with thelocation of the beam destinations.
bulky beam dumps. Radiation transport calculations were
performed to design the beam destinations, to quantify thebeam-induced activation, to enable the SCL installation inparallel to the NCL commissioning, and for dismantling purposes within a few weeks of cool-down. Thermo-mechanicalsimulations were fundamental to define the operational limits in planned, unplanned and potential failure scenarios.
The control system was based on EPICS [2] and enabled
the successful operation of all the beam destinations that
required water cooling, motion in/out of the beam line, HV
to suppress secondary electrons, timing synchronization andthe data acquisition. The proton current was measured between 0.1 mA to 62.5 mA with an accuracy of better than
1% and a time resolution better than 1μs. In this paper, highlights and key references are given for each unique beam
destination.

SOURCE TUNING WITH THE LEBT FC
The beam destination in the Low Energy Beam Transport(LEBT) section of the ESS linac was designed at ESS andmanufactured by Pantechnik [3]. It contributed to the testof the ESS source at the INFN LNS in Italy, and then to the
LEBT commissioning at the ESS. It can withstand 2.86 ms
long pulses of 75 keV protons at the nominal current and
14 Hz (see Fig. 2, with pulses acquired during the first testof the LEBT chopper at 12 kV). For instance, the optimal
source settings were found with the LEBT beam destinationby scanning five key parameters [4]: the three coils confining the magnetic field inside the plasma chamber within
the ESS source, the input RF power to the magnetron andthe hydrogen flux. Moreover, the LEBT beam destination
quantified the impact of the source repeller on the spacecharge compensation in the extraction region [5].
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THE FOUR BEAM DESTINATIONS FOR THE COMMISSIONING OF THE
ESS NORMAL CONDUCTING LINAC

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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J. Lastow†, A. Farshidfar, A. Abujame, A. Nordt, A. Andersson, A. Petrushenko, C. Webber,
D. Plotnikov, D. Daryadel, J. Gustafsson, J. Grönvall, L. Nunes, M. Zmuda, M. Carroll,M. Eriksson, M. Mansouri, N. Naicker, P. Holgersson, R. Foroozan, V. Harahap, Y. Takzare
European Spallation Source ERIC, Lund, Sweden
Abstract
The European Spallation Source (ESS) is a state-of-theart research facility currently under construction in Lund,
Sweden. Upon project delivery, ESS will host the mostpowerful linear proton accelerator and a spallation target
capable of producing the brightest neutron source in theworld. In order to enable safe commissioning and operationof these potent systems, each system has a dedicated personnel safety system (PSS). Together they make up the
ESS PSS, an integrated system of several PSS across thefacility. These systems communicate with each otherthrough a centralised interlink system, and together determine if the facility is ready for proton beam generation in
the Accelerator and consequently neutron production at theTarget Station. This paper provides a summary of the innerworkings, along with a discussion on the approach and proposed strategies for overcoming the identified challenges.

INTRODUCTION
The European Spallation Source (ESS) facility consistsof three main parts: the accelerator, target station, and asuite of neutron instruments.
The ion source, which is the first part of the accelerator,
generates protons through evaporating electrons from hydrogen gas. The protons are then lead through normal conducting and superconducting accelerating structures toreach 96 % of the speed of light. The proton beam is thendirected through a dogleg with bending magnets to the target station, which is referred to as Beam on Target (BoT).
During normal operation, this is the primary beam destination. However, in certain circumstances, the beam may bedirected to beam stops distributed in the accelerator tunnel.
At the target station, the high-energy protons collide with arotating tungsten target wheel, which releases neutrons
through spallation. The neutron beams are then moderated,
tuned and guided through a shielding structure (referred toas the Bunker) to experimental stations referred to as neutron instruments. There, researchers can use the particles as
a probe for studying the inner structure, as well as the dynamic behaviours, of a selected sample for a broad rangeof scientific fields and endeavours. The initial instrument
suite consists of 15 neutron instruments and one test beamline [1].
There are a number of hazards related to these systems,
mainly radiation-related hazards such as prompt ionizing
radiation from the proton beam and neutron beams, andgamma radiation from the target and moderators. ESS employs systems and administrative procedures to ensure the___________________________________________† jessica.lastow@ess.eu

MOPB: Monday Poster Session
MC3.4 Proton linac projects

safety of personnel in the presence of radiation. In this regard, the key systems are the personnel safety systems(PSS). They are primarily safety interlock systems, which
ensure that sources of prompt radiation are switched off toprotect personnel in beam enclosures (e.g. accelerator tunnel, experimental stations, etc.) from exposure to prompt
radiation, prevent entry to beam enclosures while sources
are energized, and switch them off when designated predefined access functions are violated. Each part of the machine has a dedicated PSS: Accelerator PSS (ACC PSS),
Target Station PSS (TS PSS), Bunker PSS, and several Instrument PSS. The full scope of PSS also includes e.g. accelerator test stands.

BACKGROUND
The PSS are designed consistently across the ESS facility in order to reduce design, installation, commissioning
and maintenance cost and effort, and more importantly to
improve system reliability. Each PSS is built using fail-safe
Programmable Logic Controllers (PLC) and distributed Input/Output (I/O) modules with redundant sensors and actuators. Safety Instrumented Functions (SIF) are derived
from the risk assessment and hazard analyses process, following the functional safety standard IEC 61511 [2]. The
boundaries of the area in which PSS is responsible for mitigating designated hazards, i.e. PSS controlled areas, arealso defined in the process. The SIFs are defined to e.g.
switch off the hazardous equipment if an intrusion into thearea is detected by the position monitoring switches on theaccess doors, or if an emergency switch-off button (ESOB)
is pressed. For example, regarding an instrument PSS thatentails closing a beam shutter (or instrument shutter) toblock neutron particle flow to the experimental station.
There are also SIFs related to radiation monitors that interface the PSS, e.g. a radiation monitor by the instrument
shutter verifies the shielding integrity of the shutter when
it is closed. If these radiation monitors alarm, the hazardous
equipment is also switched off.

INTEGRATED SYSTEM
The personnel safety systems at ESS operate independently to support the safe operation of various parts ofthe machine and neutron instruments. However, they needto also work in concert to mitigate designated hazards.
Most hazard controls methods are implemented locally, but
in certain circumstances, a PSS requires to escalate an issue
to ESS PSS and switch off the proton beam to target. The
systems need to communicate with each other, and together
determine if the facility is ready for proton beam genera-

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INTEGRATED APPROACH FOR ESS PERSONNEL SAFETY SYSTEMS

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BEAM LOSS MECHANISMS IN THE PIP-II LINAC AND BEAM
TRANSFER LINE AT FERMILAB∗
Abhishek Pathak† , Olivier Napoly, Fermi National Accelerator Laboratory, Batavia, IL, USA
Abstract
Beam loss in high-intensity H- linacs, such as the PIP-II
linac at Fermilab, is a critical challenge that requires comprehensive study and understanding to ensure efficient andsafe operation. This study explores the various beam loss
mechanisms encountered in the PIP-II linac and its beamtransfer line, drawing parallels from other high-intensity Hlinacs. Key loss mechanisms include residual gas stripping,where H- ions interact with residual gas molecules leading
to electron detachment; field s tripping, c aused by t he interaction of H- ions with magnetic fields; and intra-beam
stripping, resulting from interactions within the beam itself.
Beam halo formation, particularly due to Twiss function mismatch, is another significant source of beam loss, which canbe exacerbated by Landau damping mechanisms. Adheringto the 1 W/m loss criterion is essential to maintain hands-on
maintenance capability and ensure the longevity of the accelerator components. By understanding these mechanisms
and implementing targeted mitigation strategies, the PIP-II
linac can achieve its design goals while maintaining safe andefficient operations.

INTRODUCTION
The Proton Improvement Plan-II (PIP-II) [1] at Fermilab features an 800-MeV superconducting linear accelerator (Linac) and a comprehensive beam transfer line [2] toenhance H- delivery to the Booster (see Fig. 1). The
superconducting Linac, composed of continuous wave(CW)-capable struc-tures and cryomodules, operates withan average H− beam current of 2 mA and accelerating thebeam from 2.1 MeV to 0.8 GeV.
At such high beam intensities, beam transmission is ofgreat concern, as the beam loss mechanisms in an H- linac
like PIP-II are more numerous than in a proton linac. someof the primary sources of the beam loss in a H- ion linac
involves Intra-beam stripping, magnetic stripping, gas stripping, black body radiation, RF transienet from the ion source,
dark current from ion source, H+ capture and acceleration,and beam halo formation followed by beam mismatch along
different section of the linac or along the Beam Transfer
Line. This article primarily investigates three of these mechanisms: intra-beam stripping, magnetic stripping, and beam
halo formation due to beam mismatch.
∗ This manuscript has been authored by Fermi Research Alliance, LLC

under Contract No. DE-AC02-07CH11359 with the US Department ofEnergy, Office of Science, Office of High Energy Physics.
† abhishek@fnal.gov
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Figure 1: Schematic layout of the PIP-II Linac and associatedbeam transfer line: The diagram illustrates the 800 MeV SRF
Linac, warm front end, H− ion source, beam transfer line,
and the connection to the FNAL Booster.

INTRABEAM STRIPPING
Intrabeam stripping is a key beam loss mechanism in highintensity H− ion accelerators, occurring when electrons are
stripped from H− ions due to Coulomb interactions within
the beam. This process can result in the production of neutralhydrogen atoms (H0 ) or protons (H+ ), leading to potential
beam losses.
The probability of intrabeam stripping per unit length,
𝑃strip , is given by:
𝑃strip = 𝑁 ·𝜎strip· 𝐹 (𝑣 rel )28𝜋 𝜎𝑥 𝜎𝑦 𝜎𝑧 𝛾 2(1)where 𝑁 is the number of particles per bunch, 𝜎strip is the
stripping cross-section, 𝜎𝑥 , 𝜎𝑦 , and 𝜎𝑧 are the RMS beam
sizes, 𝛾 is the Lorentz factor, and 𝐹 (𝑣 rel ) is a form factor
that depends on the relative velocity between particles.
The stripping cross-section 𝜎strip is expressed as:
𝜎strip =𝐶𝑣 2rel(2)where 𝐶 is a constant dependent on the beam parameters, and 𝑣 rel is the relative velocity between particles. The
form factor 𝐹 (𝑣 rel ), which accounts for the distribution ofvelocities within the beam, is:!
√© 𝑣𝑥 + 𝑣𝑦 + 𝑣𝑧
ª
2− 3
­ √︃
𝐹 (𝑣 rel ) = √ √− 1®® + 1­
3( 3 − 1)𝑣 2 + 𝑣 2𝑦 + 𝑣 2𝑧
« 𝑥
¬

(3)

Analysis of the PIP-II superconducting linac and BeamTransfer Line shows that the fractional particle loss rate, total
particle loss, fractional power loss, and cumulative power
loss are within acceptable limits. As illustrated in Fig. 2, thefractional particle loss rate ( 𝑁1 𝑑𝑑𝑠𝑁 ) and integrated particle
MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB050

A. Sukhanov†, C. Contreras-Martinez, C. Grimm, B. Hanna, B. Hansen, S. Kazakov,
T. Khabiboulline, M. Parise, D. Passarelli, Y. Pischalnikov, D. Porwisiak, V. Roger, J. Subedi,
A. Syed, P. Varghese, S. Wijethunga, V. Yakovlev, Fermilab, Batavia, IL, USA
Abstract
As part of the PIP-II project at Fermilab, a pre-production cryomodule featuring 325 MHz Single Spoke Resonator type 2 (SSR2) superconducting RF cavities is underconstruction. These SSR2 cavities are fabricated by industry partners and undergo initial cold testing at our collaborating institution, IJCLab in France, utilizing low-power
coupler. Subsequently, the cavities are subjected to final
qualification at Fermilab, complete with tuner and highpower coupler assemblies. This paper provides an overview of the ongoing efforts dedicated to high-power testingof jacketed SSR2 cavities in the Spoke Test Cryostat (STC)
at Fermilab. Performance parameters obtained from thesetests are presented, offering valuable insights into the cavities’ operational characteristics and readiness for integration into the PIP-II cryomodule.

cross-check testing procedures between different test setups in our institutions. Five such tests were performed on
two cavities [3]. One SSR2 pre-production cavity was delivered to Fermilab recently from another vendor. Initial
performance evaluation of this cavity was performed at
STC in LPC setup.
After initial verification, cavities were assembled withhigh-power coupler and tuner. In this paper we report on
ongoing efforts of HPC testing of SSR2 cavities at STC.

INTRODUCTION
The Proton Improvement Plan-II project (PIP-II) is built
at Fermilab to deliver intense neutrino beam to LBNFDUNE experiment [1]. PIP-II utilizes continuous-wave(CW) Superconducting RF (SRF) linac to accelerate Hions up to 800 MeV. For efficient performance PIP-II linac
is composed of five different types of cavities. Thirty fiveSingle Spoke Resonator Type-2 (SSR2) cavities operating
at 325 MHz and assembled in seven cryo-modules accelerate beam from 35 to 185 MeV [2].
Seven pre-production jacketed SSR2 cavities were fabricated by the Fermilab industry partners. Six of these cavities from one of the vendors were initially cold tested at
IJCLab in France with low-power coupler (LPC). Resultsof this testing were discussed elsewhere [3]. SSR2 cavities
from IJCLab and one from the second vendor were delivered to Fermilab for assembly with tuner and high-power
coupler (HPC) and final testing and qualification at the Fermilab Spoke Test Cryostat (STC) before installation into
the pre-production SSR2 cryo-module.
The Fermilab STC facility (see Fig. 1) is capable ofcold testing of four out of five types of PIP-II SRF cavities:
both 325 MHz SSR type 1 [4] and type 2, and 650 MHz 5cell elliptical Low and High beta (LB650, HB650) cavities [5]. RF tests at STC could be performed in LPC and
HPC configurations. Initially, SSR2 cavities received at
Fermilab from IJCLab, were tested with LPC to verify and___________________________________________* This manuscript has been authored by Fermi Research Alliance, LLC
under Contract No. DE-AC02-07CH11359 with the U.S. Department ofEnergy, Office of Science, Office of High Energy Physics.
† ais@fnal.gov
MOPB: Monday Poster Session
MC4.8 Superconducting RF

Figure 1: Spoke Test Cryostat facility at Fermilab.

STC TEST SEQUENCE
Cavity Preparation and Installation
Jacketed SSR2 cavities were shipped to Fermilab assembled with LPC and under vacuum in RF/beamline volume.
When no verification with LPC at STC were required, orafter the STC LPC testing, cavities underwent installationof high-power coupler [6]. Cavities assembled with HPC
were delivered to STC for installation of tuner and instrumentation. Typical instrumentation setup included temperature sensors at the cavity Helium vessel (top, bottom, middle), tuner arm and motor windings, coupler ceramic window flange and 5 K and 80 K intercepts; magnetic sensors
at the vessel and beam pipe; heater at the coupler ceramic
window flange. Subsequently, cavities were inserted into
the STC cryostat, Fig. 2, where air (warm) side of the coupler was assembled and connected to the RF distribution
system and thermal connection of the coupler 80 K intercept to the STC high-temperature thermal shield (HTTS)
was done. Note, that because STC did not have low-temperature thermal shield, coupler 5 K intercept was not connected. After making cryogenic and beamline vacuum
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COLD TEST RESULTS OF PRE-PRODUCTION PIP-II SSR2 CAVITIESWITH HIGH-POWER COUPLERS IN THE
FERMILAB SPOKE TEST CRYOSTAT*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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HIGH ORDER MODES SPECTRA MEASUREMENTS
IN 1.3 GHz CAVITIES FOR LCLS-II*
A. Lunin†, T. Khabiboulline, A. Sukhanov, V. Yakovlev, Fermilab, Batavia, USA
Abstract
Fermilab recently completed production and testing of
1.3 GHz cryomodules for the LCLS-II project. Each cryomodule consists of eight TESLA-shaped superconducting
elliptical cavities equipped with two High Order Mode
(HOM) coupler ports. Measurement of the HOM spectrum
is part of the incoming quality control of cavities at room
temperature and the final qualification cold test of cryomodules at the Cryomodule Test Facility (CMTF). In thispaper we describe the procedure for measuring the HOM
spectrum along with further data processing. Finally, we
present accumulated statistics of individual HOM frequencies and quality factors related to various cavity vendors
and discuss the possible contribution of HOMs to heatloads and beam dynamics.

INTRODUCTION
Advances in superconducting technologies result in realization of many projects of particle accelerators operating both in continuous mode and in modes with high duty
factors of the beam current (XFEL, LCLS-II, ILC). Superconducting (SRF) cavities are a good resonant system witha spectrum of modes having very high-quality factors. A
beam of charged particles can potentially cause resonant
excitation of a particular High Order Mode (HOM) andlead to both large beam power losses and dilution of thebeam emittance. Due to the nature of SRF cavities, they
have a random eigen spectrum, and coherent HOM excitation becomes an inherently probabilistic problem that isvery difficult to evaluate [1]. Note that knowing the exact
HOM stochastics, we can estimate the regenerative beam
breakup instability, which is critical for machines with highbeam current. Thus, direct measurement of the HOM parameters under operating conditions allows us to obtain areliable model of the interaction of the beam with thecavity HOM spectrum. In addition, monitoring HOM spectra allows any deviations to be identified earlier and notifies the supplier of non-conforming cavity fabrication.
As part of the LCLS-II collaboration, Fermilab was responsible for the production and testing of twenty 1.3 GHz cryomodules [2]. For technological purposes, two independent companies (vendor A and vendor B) with approximately equal contributions were selected to manufacture
SRF cavities. When a cavity is received from a vendor, it
follows standard cryomodule assembly procedures, including a series of incoming quality checks (QC). Figure 1
shows the workflow for final assembly of the LCLS-II cryomodule in the high-bay ICB building and subsequent highpower RF testing at the dedicated Cryomodule Test Facility (CMTF) at Fermilab. Measurements of the HOM spectra of the cavities were taken during tests in the CMTF after
the cooling the cryomodule to 2K and tuning all fundamental power couplers (FPC) to a nominal external coupling of
4E7. After post-processing the raw data, the sorted HOM
parameters are recorded in the online traveller database foreach delivered cryomodule.

RF MEASUREMENTS OF HOM SPECTRAThe layout of the 9-cell 1.3 GHz cavity for the LCLS-II
project is illustrated in Fig. 2. The cavity has an FPC port
and three auxiliary ports, including two downstream andupstream HOM couplers. To measure the HOM spectrum,
we recorded signal transmission from HOM1 ports to
HOM2 ports. Since the cryomodule is being tested inside a
concrete cave used as radiation shielding, there are approximately 20 meters of ⅜-inch diameter Heliax coaxial cables
connecting the auxiliary ports to the low-power electronics
rack located outside the cave. These HOM cables were
temporarily used to connect to the vector network analyser(VNA) ports to measure the S21 transmitted signal. TypicalFigure 1: LCLS-II cryomodule assembly workflow at a series of workstations (WS) in the high-bay ICB building andfinal RF testing in the CMTF facility at Fermilab.
____________________________________________* Work supported by Fermi Research Alliance, LLC under Contract
No. DE-AC02-07CH11359 with the U.S. Department of Energy† lunin@fnal.gov
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SUCCESSFUL CLEANROOM INSTALLATION OF PIP-II SSR2 COUPLER
USING ROBOTIC ARM ∗C. Narug† , D. Passarelli, G. Wu, M. Parise, T. Aiazzi,
D. Bice, J. Helsper, Fermilab, Batavia, IL, USA
C. Denton, Northern Illinois University, Dekalb, IL, USA
A. Ciaramella, University of Pisa, Pisa, Italy
Abstract
To minimize the risk of contamination during the assembly of SRF cavities, remote installation techniques areneeded. Recent developments at Fermilab have initiated theprocess of employing robotics for cavity assembly. Various alignment strategies were prototyped and evaluated. A
remotely controlled robotic arm was successfully used toalign and install couplers on prototype PIP-II SSR2 cavities
in a cleanroom environment. This process highlights thepotential for extending these techniques to the installationof other cavities and associated components in the future.

test station outside of the cleanroom. This test station wasconstructed using the same components as the final setup, including cavity supports and rail systems, to closely replicate
the cleanroom environment. Multiple test assemblies were
performed using 3D-printed components, which allowed forthe rapid iteration and evaluation of designs for attaching
the coupler to the robotic arm and supporting the cavity on
the structure. The flexibility of 3D printing enabled quick
modifications, providing valuable insights before producing
cleanroom-compatible components. The layout of the test
station is shown in Fig. 1.

MOTIVATIONTo reduce the risk of contamination on the superconducting surfaces of SRF cavities, specialized assembly toolingsets are typically employed to attach components in a cleanroom environment. Each new assembly application often
necessitates the development of a unique set of tooling andcorresponding procedures. Despite efforts to standardize
tooling across projects [1], contamination risks persist, primarily due to manual operation and adjustments by technicians. To address this issue, Fermilab has initiated work on
utilizing robotic arms for the assembly of Superconducting
Radio Frequency (SRF) cavities, aiming to significantly minimize contamination. The first intended application for thisassembly process is the assembly of couplers onto the Proton
Improvement Plan-II (PIP-II) Single Spoke Resonators Type
2 (SSR2) cavities.

ASSEMBLY CELL
When selecting a suitable robotic arm, key considerations
included safety features, cleanroom compatibility, payload
capacity, and ease of use. After evaluating the options available on the market, a 6-axis robotic arm was chosen. This
cobot, with a payload capacity of 16 kg, is certified for use
in cleanrooms up to ISO 14644-1 Class 5. The robotic arm
also come equipped with various safety features, remotecontrol capabilities and force-sensitive tool flanges that allow the arm to stop automatically in the event of a collision.
Additionally, the arm can be programmed via an attachedtablet, which reduces the development time for specific applications [2].
In preparation for testing assembly methods on the actual
SRF cavity, an initial assembly was conducted at a dedicated∗ Work supported by Fermi Research Alliance, CONF-24-0248-TD† cnarug@fnal.gov

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Figure 1: Test station setup for initial robotic assembly trials.
Using these prototype components, four potential assembly processes were developed. These methods were used tocreate a series of pre-programmed waypoints for the roboticarm, which would later be applied in the cleanroom. Before
relocating the setup to the cleanroom, a successful assembly was carried out using a plastic cavity and coupler, as
well as with a prototype coupler and a prototype cavity that
required reprocessing. The effectiveness and specifics ofeach of these methods will be discussed in detail later in thispaper.

INSTALLATION PROCESS
Using the procedure developed at the test station, theinstallation of the coupler onto the cavities was performed
in a cleanroom at Fermilab. To prepare for assembly, allcomponents were thoroughly cleaned before being brought
into the cleanroom. The coupler was then mounted onto therobotic arm using a set of L-bracket tooling, with alignment
pins installed on the flange of the coupler.
To prepare the cavity for the installation, four bolts were
removed from the flange, which was then blown with purenitrogen to eliminate any particles. The robotic arm wasused to position the coupler and align it with the cavity. Thisaligned position was saved as a waypoint. Afterward, the
MOPB: Monday Poster Session
MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB057

C. Narug† , M. Parise, D. Passarelli, L.Ristori, H. Park,
V. Rogers, J. Helsper, Fermilab, Batavia, IL, USA
C. Denton, I. Salehinia, Northern Illinois University, Dekalb, IL, USA
Abstract
For assemblies of cavities in cleanrooms, single-use tooling systems are made for the alignment and installation ofancillary components such as couplers and bellows. To
minimize the number of tooling sets created, a design has
been created to standardize alignment features to allow for
assembly of different components with one set of tooling.
A prototype set of tooling has been developed to with therequired degrees of freedom for multiple assemblies while
minimizing deformation during the assembly process. Prototype designs have been created for PIP-II SSR2 and 650
Cavities and for AUP Crab Cavities. Using 3D printing,this tooling can be quickly adjusted to allow for different
ancillary components. The development process and statusof the design will be discussed.

INTRODUCTION
In the pursuit of higher gradient Superconducting Radio
Frequency (SRF) cavities, there is a need to further reduce
contamination inside superconducting cavities. One of the
primary sources of contamination occur during the installation of ancillary components during production. To reduce
sources of contamination, alignment tooling is used to support components while increasing the distance of people
to the open cavities. To serve as backups for the robotic
assembly procedures being developed [1], a set of universal
component installation tooling has been developed. The primary purpose of the redesign of the tooling was for the Proton Improvement Plan-II (PIP-II) Single Spoke Resonators
Type 2 (SSR2) Cavities. For this project the tooling was initially designed for the only the coupler installation processes.
Additional requirements by the PIP-II project required expanding the use of the tooling for installing 650 MHz cavity
coupler assemblies. Additional design feedback has been
received from projects, such as for the High Luminosity
LHC Accelerator Upgrade Project’s (AUP) Crab Cavities.
Feedback and design details have been refined to allow thetooling to be used for all of the projects and future projects
to allow for the tooling to be used with minimal functionalchanges.

specific issues faced with the tooling were that there were
too many points of adjustment, the structure was unstable,
and the internal mechanisms limited the orientation of thecomponents.
Expanding on some of the limitations, the adjustment
mechanism in the tooling had redundant points of contactact
for aligning components. For example, to the horizontal
position was held and aligned using two threaded rods. Thismechanism required tightening and loosening threaded rods
to gradually shift the coupler horizontally and vertically.
The multiple adjustable mechanisms led to a design thatwas inherently unstable and which had difficulty supporting
components. The mechanisms also limited theDue to the combination of adjustment features used, theorientation of the adjustment assembly was limited. The
mechanism that was most limited by these features was themechanism that pushed the assembly along the track. The
mechanism was a threaded rod with a foot that pushed themain alignment tooling along the track. While the mechanism did allow for smooth sliding as the foot was not fixed tothe main alignment tooling, it also made the mechanism unable to support different orientations and required the device
to be mounted at 45 degrees. These limitations in the initialtooling design were the initial motivation for redesigning
the overall tool design.

Previous Tooling
The intial set of tooling was developed exclusively foruse for the installation of SSR2 couplers. This tooling canbe seen in Fig. 1. The tooling had multiple drawbacks thatmade it difficult to use in a production environment. The

Figure 1: Initial SSR2 coupler alignment tooling.

∗ Work supported by Fermi Research Alliance, CONF-24-0249-TD† cnarug@fnal.gov

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STANDARDIZATION OF ANCILLARY INSTALLATION TOOLING FORSRF CAVITIES AT FERMILAB ∗32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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TESTING OF THE SSR2 SRF CAVITY TUNER FOR PIP-II at 2 K*
C. Contreras-Martinez†, A. Sukhanov, P. Varghese, M. Parise, Y. Pischalnikov,
J. Holzbauer, D. Passarelli, V. Roger, Fermilab, Batavia, IL, USA
Abstract
The PIP-II linac will include thirty-five 325 MHz Single
Spoke Resonators Type 2 (SSR2) cavities. Each cavity will
be equipped with a tuner for resonance control. The tuner
consists of mechanical frame with a motor for coarse frequency tuning and a piezoelectric actuator for fine frequency tuning. The tuner was tested for the first time at
Fermilab on an SSR2 cavity. This dressed cavity-tuner system was tested at the single spoke testing cryostat (STC) in
Fermilab at 2 K. The tuner performance was evaluated andis presented. Lastly, cavity-tuner mechanical modes were
measured via the piezos.

INTRODUCTION
The SSR2 cavities are one of five classes of superconducting RF (SRF) cavities that will form part of the proton
improvement plan (PIP)-II linac under construction at Fermilab. The cavities use an SRF tuner to keep them on resonance to accelerate the beam to the specified energy efficiently. The cavity will use a double lever tuner which issimilar in design to the SSR1 tuner [1]. It can compensate
for slow-coarse frequency detuning as well as fast-fine frequency detuning.
The tuner can only compress the cavity; therefore, thefrequency of the warm cavity is set to have a positive frequency offset of ≤130 kHz (see Table 1) when cooled to2 K. The slow-coarse frequency component of the tuner,
composed of a stepper motor, is used to compensate for thisdeviation. Microphonics and helium pressure fluctuation
require the use of a fast-fine frequency tuning component.
The fast-fine tuner component consists of two piezoelectric
actuator capsules. Accelerated lifetime and irradiation tests
at Fermilab demonstrate that the stepper motor and piezo
will survive prolonged operation far exceeding the typicallinac lifetime of 25 years [2,3].
The frequency tuner performance was measured when
the SSR2 cavity was cooled to 2 K. Additionally, the mechanical modes of the cavity-tuner system were measured
via the piezos. The cavity was placed in the Spoke Resonator Test Cryostat (STC) facility at the Meson Detector
Building (MDB) at Fermilab, pictured in Fig. 1. The results
are compared to the project specifications [4] and to theresults from the Irène Joliot-Curie laboratory (IJCLab) testin France [5].
____________________________________________*This manuscript has been authored by Fermi Research Alliance, LLC
under Contract No. DE-AC02-07CH11359 and DE-AC02-76SF00515
with the U.S. Department of Energy, Office of Science, Office of HighEnergy Physics.
†
ccontrer@fnal.gov
MOPB058
170

Figure 1: 325 MHz SSR2 cavity with tuner and other ancillaries installed at the MDB facility.

SLOW-COARSE TUNING COMPONENT
Pivoting Motor Lever Dislocation
After installing the tuner on the cavity the tuner probe
gap was set to 1 mm. This gap is between the two probes
on the tuner arms and cavity. The purpose of the gap is to
avoid any excessive compression of the cavity by the tuner
during cool down and measure the frequency change of thecavity solely due to cool down effects. The initial frequency (shown as 0 position in Fig. 2) is the frequency due
to cool down effects (tuner was disengaged). An estimateof 60 k steps is needed to close the 1 mm gap between theprobes and cavity (though due to cooldown effects it was
expected to be less). During initial motor checks prior toclosing the cryostat the shaft turning direction waschecked. Applying negative steps to stepper motor will
move the tuner probes to compress the cavity.
Once the cavity was cooled to 2 K the motor was actuated with minus 60 k steps and tuner probes must have
moved by ~1 mm (see Fig. 2 named 1st movement). However, the cavity frequency did not change. After not seeinga response from minus 60 k steps doubt settled that the perhaps the wrong motor direction was applied. Positive steps
were then used and after plus 60 k steps from 0 steps (seeFig. 2 second movement) no response was observed. The
original direction (negative steps) was tried again.
After operating the stepper motor for minus 120 k steps
from the 0th position the probes compressed the cavity (seeFig 2). The number of steps from the 0th position until firstcontact translates to 2 mm on the gap (See Fig. 2). After

MOPB: Monday Poster Session
MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB060

E. Chen, R. Sharankova, A. Shemyakin, J. Stanton
Fermi National Accelerator Laboratory, Batavia, USA
Abstract
The Fermilab Side-Coupled Linac accelerates H- beamfrom 116 MeV to 400 MeV through seven 805 MHz modules. Twelve wire scanners are present in the Side Coupled
Linac and four are present in the transfer line between the
Linac and the Booster synchrotron ring. These wire scanners act as important diagnostic instruments to directly collect information on the beam’s transverse distribution. The
manipulation of the conditions of wire scanner data collection enables further characterization of the beamline, suchas calculating emittance and the Twiss parameters of thebeam at select regions, which we present here.

INTRODUCTION
The Fermilab Side-Coupled Linac accelerates
116.5 MeV H- beam to 400 MeV via 805 MHz side-coupled cavities [1]. The cavities are organized into sevenmain modules (Modules 1-7) with four sections in each
module, as well as a transition section (Module 0) composed of 805 MHz buncher (B) and Vernier (V) cavities,
Fig. 1.

Figure 1: Schematic of the Fermilab Side-Coupled Linac
and representative layout inside Module 2. Naming convention for diagnostic instruments follows the structure of
Qmn (quads, green dots) or Dmn (WSs, orange diamonds),
where m = module number and n = section number.
Diagnostic, steering, and focusing elements are present
in between sections and modules, including an alternating
FODO lattice of quadrupoles [1] and 12 wire scanners(WSs) throughout the Side-Coupled Linac [2]. The WSs
yield transverse profiles in the X and Y directions (Fig. 2),
as well as in a 45° direction not discussed here.
The abundance of these diagnostic devices in the SideCoupled Linac facilitates the use of WSs to measure thetransverse emittance and the Twiss parameters of the Hbeam. Such measurements have not been performed in
more than a decade [2]; however, we seek to experimentally characterize the present state of the Fermilab Linac.
Here we present the results of the recent study analyzing
transverse beam properties in the Side-Coupled Linac.
___________________________________________* This manuscript has been authored by Fermi Research Alliance, LLC
under Contract No. DE-AC02-07CH11359 with the U.S. Department ofEnergy, Office of Science, Office of High Energy Physics.
MOPB: Monday Poster Session
MC4.1 Beam diagnostics

Figure 2: Example of vertical (Y) wire scans from quadrupole scan Q54-D63 with Q54 at 80 A and 120 A.

MEASUREMENTS OF EMITTANCE ANDTWISS PARAMETERS
The transverse emittance and Twiss parameters were
measured via two methods: a quadrupole scan and a beamwidth measurement at several locations in a drift space.
To reduce the duration of the wire scans, the scan procedure was modified to run at a constant speed. Previously,
the wire frame was moved in steps, requiring significant
time to equilibrate at each position and an overall scan timeof 10-15 minutes. This long scan time is incompatible witha quadrupole scan, in which a large number of wire scans
is required. Instead, the modified procedure collects position and intensity data on each beam pulse while moving
the wires at a constant speed across the beam pipe, reducing scan time tenfold to 1.25 minutes and demonstratingcomparable data quality [3]. The step in space between the
points is defined by the wire frame speed and pulse frequency. To address the low signal-to-noise ratio, the beamprofile width is characterized by the standard deviation of
the fitted Gaussian function 𝜎 . The use of beam widthfrom the Gaussian fit additionally allows inclusion of scanswith incomplete beam profiles due to insufficient scan
range. The RMS errors associated with the Gaussian fit areassigned to all points shown in Figs. 3 and 4. A Python program was written to schedule the wire scans and vary thequadrupole current for the quadrupole scan, enabling fastercollection.
Data for both methods were collected in July 2024 with18.7 mA beam at the output of the Linac and 5 Hz pulse
frequency. For the quadrupole scan, wire scans taken whenmoving the frame both “in” and “out” of the beam pipewith a 5 μs pulse length. For the propagation in free spaceexperiment, data were taken in both the “in” and “out” directions and averaged.

Quadrupole Scan
In the thin-lens approximation, the quadrupole scan isdefined by the characteristic equation in Eq. (1).

MOPB060
173

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EMITTANCE MEASUREMENTS WITH WIRE SCANNERS
IN THE FERMILAB SIDE-COUPLED LINAC *32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB061

S. K. Suthar∗ , B. Popovic
Accelerator Systems Division, Argonne National Laboratory, Lemont, IL, USA
Abstract
In accelerator physics, radio-frequency (rf) systems playa pivotal role in particle beam acceleration and diagnostics. This work presents a graphical interface designed withPython for interaction with rf instruments, enabling efficient
data acquisition, processing, and visualization. Leveraging
advanced software tools, the system enables efficient management and analysis of rf data. This capability is crucial for
optimizing experimentation and streamlining data flow. The
modular architecture is implemented on various systems
and is demonstrated with the current 200kW Solid State
Amplifier (SSA) test setup at the Advanced Photon Source.

INTRODUCTION
Measurement and characterization of rf systems involve avariety of instrumentation, but retain the fundamental process of experimentation: measurement, acquisition, processing, and modelling. The Advanced Photon Source (APS)
has a variety of rf systems and structures in operation. To
streamline interfacing with these systems, instrumentation
can be automated and centralized. Creating these capabilities allows for powerful organization and handling of rf data,
which is important for advanced characterization.

METHODOLOGY
Python is employed as the primary development tool
for this project. Libraries such as vxi-11, pyvisa, and rsinstrument are used for instrument communication. For dataprocessing matplotlib, numpy, and an in-house rf-based toolboxare used. This choice of software provides compatibility
and modularity for the proposed use case. Furthermore,streamlining, centralizing, and automating data acquisition
for rf instruments allows for an organized scheme to characterize rf systems. Additionally, industry standard touchstone
files are supported for import and exportation of scatteringparameters.

Figure 1: Instrument and experiment modules Left: Experiment module for running sweeps, Right: Settings module
for instrument parameter control, Bottom: Instrument connection interface.
As seen in Fig. 2, the plotter module facilitates the analysis
of scattering parameter data. A multitude of parameters canbe derived from datasets and visualized in various different
plot types. Also, various traces and measurements can beoverlapped to allow for comparative analyses.

DEVELOPMENT
Figure 1 shows some modules of the full GUI. The developed software tool contains modules to interface with many
instruments including: Vector Network Analyzers (VNAs),
pulsed and CW power meters, and signal generators. By
using standardized instrumentation protocols, implementing support for additional instruments can be done easily.
Additionally, the system incorporates various functions toprocess and visualize data.
∗ sohumksuthar@gmail.com | ssuthar@anl.gov

MOPB: Monday Poster Session
MC4.7 Room temperature RF

Figure 2: Reader-friendly plotter module.
MOPB061
177

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DATA ACQUISITION AND CHARACTERIZATION SOFTWARE FOR
RADIO-FREQUENCY (RF) SYSTEMS

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB062

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

GRIDDED RF GUN DESIGN FOR SRF LINAC APPLICATIONS
I. Gonin†, C. Edwards, S. Kazakov, T. Khabiboulline, T. Nicol, A. Saini, N. Solyak,
J.C.T. Thangaraj, V. Yakovlev, FNAL, Batavia, IL, USA
M. Curtis, K. Gunther, HeatWave Labs, Inc., Watsonville, CA, USA
Abstract
The thermionic gridded gun is described which generates short electron bunches for further acceleration in a
Nb3Sn conduction cooled SRF linac. The gun is built into
the first cavity of the 250 keV injector [1] for the 20 kW,
10 MeV, 1.3 GHz CW conduction cooled one-cavity linac.
The beam current is 2 mA. The RF gun design is presented
as well as the results of perveance measurements, which
are in a good agreement with the design parameters. The
design of the RF resonator of the gun is presented also. The
beam generated by the gun is matched to the injector toprovide lack of current interception in the SRF cavity.

GENERAL
The concept of compact linear electron accelerators forindustrial application suggested in [2] is based on use of
Nb3Sn conduction cooled SRF cavities. This concept allows both high energy ≳ 10 MeV and high power of MW
level. One of the most serious limitations of the beam
power is the beam current interception in the SRF cavity
cooled by few cryo-coolers which provide power removalof ~2-2.5 W each at 4.5 K. Therefore, power loss in the
SRF cavity caused by intercepted electrons should not exceed ~1 W, or ~ 1.e-6. It means that a source of electrons
should provide short bunches without tails, which may be
defocused by RF field and reach the cavity surface. In addition, the beam should have considerably low transverse
emittance preventing strong bam diameter increase in thecavity. To generate these short bunches, we suggested touse gridded RF gun [3]. RF field is applied to the gun cathode – grid gap together with the bias deceleration DC voltage. This scheme provides electron injection in very narrow phase domain, few degrees, and therefore, generationof very short bunches. On the other hand, this scheme provides lack of long bunch tails. Initially the gun has been
designed for 650 MHz, 1.8 MeV linac prototype which isunder construction at IARC [3]. It will be installed directly
into the SRF cavity. For 1.3 GHz prototype [2] a specialroom-temperature injector has been designed [1] which
provides the 250-300 keV beam for the SRF accelerator.
This concept potentially allows higher beam power than
the scheme with immersed gun, because high power andconsequently high beam current (up to 100 mA at very
short, <10° pulses) requires considerably big cathode diameter, and therefore, large black body radiation and cavity
contamination caused by the cathode material evaporation.
The design of a thermionic electron source which can either be directly connected to a superconducting cavity or
be part of a normal conducted injector cavity is described.
___________________________________________† gonin@fnal.gov.
MOPB062180

The direct connection option is applied in a prototype 1½cell 650 MHz SRF cavity capable of delivering a 12.5 mA
average beam current with a beam power of 20 kW. As an
external option we present the development of a CW normal conducting 1.3 GHz RF injector which consists of agridded RF gun integrated with the first cell of a copper
booster cavity. The electron source concept is presented including the cathode-grid assembly and the gun resonator
design.

THE RF GUN DESIGNThe RF gun consists of the cathode-grid assembly andthe gun RF resonator. Fig. 1 show a 3D cross-section of thecathode-grid assembly [3]. The assembly contains the cathode-grid part, the transition support part, the socket partwith the ceramic window which subdivide the vacuum
cathode part and air RF resonator, and the socket.

Figure 1: Cross-section of the cathode-grid assembly.
The beam optics is determined by the shape of the grid
extension electrode with Pierce angle. It has an impregnated cathode of 612M type with a 1.8 eV work function
to provide electron current density greater than 10 A/cm2
at emitter temperature of 1050ºC. The cathode Ø = 1.5 mm
to provide low heat load (< 1W). The grid is placed at the
distance of 150 microns from the cathode. The cathode has
planar shape. The grid is attached to the Pierce angle electrode. The grid transparency is higher than 80%. Planar geometry of the cathode and grid is less sensitive to dimensional errors and misalignments. A heater filament should
be designed to avoid the heater magnetic field on the cathode. The heater power level < 2 W. The gun cathode-grid
unit engineering design is made by HeatWave Labs
(HWL).
Figure 2 shows the cathode-grid area with details of theheater. An outer conductor and the grid are grounded. The
cathode and heater are at a DC bias voltage. To minimize
the heater power, the cathode is mounted using a support
sleeve made of 25 μm (0.001”) thick molybdenum/rhenium alloy with an additional hole pattern to reduce thethermal path to emulate a 12.5 µm thick sleeve. To reduce
thermal radiation, a special thermal shield of a 25 μm thick
Mo/Re has been added to the design.
MOPB: Monday Poster Session
MC1.2 Electron and ion sources, guns, photo injectors, charge breeders

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB063

J. Bernardini† , D. Passarelli, M. Parise, V. Roger, Y. Xie, G. Romanov, F. Lewis, A. Hogberg
FNAL, Batavia, USA
Abstract
This paper outlines the strategy aimed at mitigating the adverse effects of residual magnetic fields on the performanceof pre-production SSR2 superconducting cavities within thecontext of the PIP-II project at Fermilab. Residual magnetic
fields can significantly impact cavity performance, leading
to reduced quality factor. To address this challenge, ourstrategy integrates various approaches including magnetic
shielding, careful selection of materials, quality controls
aimed at measuring magnetic permeability, magnetic hygiene to reduce residual magnetic field at the installation
phase. Additionally, experimental studies are being planned
to analyze the behavior of the cavities under different magnetic field conditions, and the effectiveness of advanced
demagnetization procedures.

INTRODUCTION
The Proton Improvement Plan II (PIP-II) project [1] at
Fermilab is an upgrade to the existing accelerator complex,
designed to power the world’s most intense high-energy
neutrino beam for the LBNF-DUNE experiment. The PIPII Linear Accelerator (Linac) features five different typesof Superconducting Radio Frequency (SRF) accelerating
cavities, each housed in distinct cryomodules (CMs) [2–4],
and equipped with high-power RF couplers and frequency
tuners:• 162.5 MHz Half Wave Resonators (HWR).
• 325 MHz Single Spoke Resonators type 1 and type 2(SSR1 and SSR2) [5, 6].
• 650 MHz 5 cells low beta and high beta (LB650 and
HB650) [7, 8].
The CMs containing the HWR, SSR1, and SSR2 cavities also include superconducting focusing lenses and beam
position monitors (BPMs). The focusing lenses are superconducting magnets that combine a solenoid with bucking
coils and four independently powered corrector coils. The
HWR focusing lenses are convection cooled in a bath of 2 K
liquid Helium, while the SSR focusing lenses are conduction cooled through copper straps thermally connecting thesolenoid and corrector coils to the 2-phase Helium returnpipe.
All PIP-II cryomodules feature a global magnetic shielddesigned to attenuate the magnetic field at the cavities’ surfaces. The acceptable magnetic field is 50 mG for HWR, 15∗ Work supported by Fermi Research Alliance, LLC under Contract No.

DEAC02- 07CH11359 with the United States Department of Energy,
Office of Science, Office of High Energy Physics.
† jbernard@fnal.gov
MOPB: Monday Poster Session
MC4.2 Cryomodules and cryogenics

mG for SSR1 and SSR2, and 5 mG for LB650 and HB650
cavities. The more stringent requirement for LB650 and
HB650 CMs is met by adding a local cold magnetic shieldsurrounding the cavities. Moreover, for the SSR1 and SSR2
CMs, all components inside the cold mass must have a relative magnetic permeability 𝜇𝑟 < 1.02 and a maximum
residual magnetic field of less than 5 mG at zero distancefrom the surface when the focusing lenses are off. Whenpowered, the focusing lenses must have a fringe field of lessthan 10 G on the surface of a cylinder, centered on the focusing lens, with a diameter of 0.7 m and a length of 0.84m.
Such requirements aim at minimizing the degradation in
the 𝑄 0 of the cavities from horizontal testing in the Spoke
Test Cryostat (STC) to CM configuration. Indeed, a 𝑄 0
degradation was observed for prototype SSR1 cavities whencomparing the results from STC to cryomodule testing [9,10].

PASSIVE MITIGATION STRATEGY
Passive mitigation techniques begin during the designphase by prioritizing the use of non-ferromagnetic materials
such as Titanium Gr. 5 and Gr. 2, Aluminum and Copper
alloys. For example, in the cavity’s helium jacket, the material was changed from SS 316L (used in the prototype SSR1
CM) to Titanium Gr. 2 (used in pre-production SSR2 andproduction SSR1 and SSR2 CMs) [11].
When austenitic stainless steel is used, it is crucial that its
relative magnetic permeability is less than 1.02. However,SS 316L (UNS S31603, EN 1.4404) does not always meetthis requirement [12]. Despite this, SS 316L remains thematerial of choice for pre-production SSR2 BPMs, edgewelded bellows, frequency tuners, and most hardware andmechanical supports used in the CM.

Relative Magnetic Permeability of Components in
SS 316L
To ensure the relative magnetic permeability of components in SS 316L stays below 1.02, solution annealing is
employed. When annealing is applicable, the process involves: initial machining of the stock material, heating to1420 K (the duration must ensure that the core of the material reaches this temperature), water quenching, and final
machining.
In case of TIG welded joints between parts in SS 316L,
ER310 and ER316LMn bare wires are used as filler material[13]. Several tests were performed by TIG welding tubes
in SS 316L, having initial 𝜇𝑟 < 1.01, with different filler
materials, results are summarized in Table 1.
MOPB063
183

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STRATEGIES FOR MITIGATING RESIDUAL MAGNETIC FIELD EFFECTON PRE-PRODUCTION PIP-II SSR2 CRYOMODULE PERFORMANCE∗J. Bernardini† , D. Dillman, S. Zorzetti, F. Lewis, M. Parise, V. Roger, D. Passarelli,Fermi National Accelerator Laboratory, Batavia, IL, USA
A. Gonzalez, Université Paris-Saclay, IRFU-CEA, Gif-sur-Yvette, France
N. Kumar, ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Harwell, Didcot, UK
Abstract
PIP-II cryomodules use a computer vision system (HBCAMs system) to monitor the alignment of SRF cavities
and focusing lenses during assembly, testing, and operation.
This contribution details the integration of the H-BCAMs
into the Spoke Test Cryostat (STC) at Fermilab, which isutilized for cold testing SRF cavities prior to their integration into the string assembly. Thermal and structural finite
element analyses were employed to estimate the cavities’
deformations, to be validated during cold testing in the STC
using H-BCAMs. Notably, this marks the first instance of
H-BCAMs integration into a cryostat and operation withina cryogenic environment.

INTRODUCTION
The geometric axes of Superconducting Radio Frequency(SRF) cavities and magnets installed in the Proton Improvement Plan II (PIP-II) [1] cryomodules (CMs) are aligned
during the string assembly phase. This alignment must be
maintained throughout the cryomodule assembly, transport,
and operational phases. The alignment requirements for cavities and magnets in Single Spoke Resonators Type 1 (SSR1)
and Type 2 (SSR2) CMs are detailed in Table 1.

ence as the CM is cooled from ambient temperature to 2 K.
Both vertical and transversal displacements of the axes ofcavities and magnets are estimated using coupled thermaland structural Finite Element Analyses (FEA) performedin ANSYS [7] and are also measured directly during cavity testing in the STC. Each PIP-II cavity, equipped with afrequency tuner and high-power RF coupler, must be coldtested and qualified in the STC before being integrated into
the CM string.
The installation of H-BCAMs in the STC enables themeasurement of target movements, which are strategicallymounted on the helium vessel of SRF cavities, during
cooldown. These displacements help determine the verticaland transversal movement of the cavity’s axis, which canthen be applied as an offset during the string assembly phase.
In Fermilab-style CMs [8–10], string components are individually mounted on support posts and interconnected byedge-welded bellows [11]. The flexibility provided by thesebellows allows for independent movement of each cavity andmagnet using a dedicated alignment system [12, 13].

Table 1: PIP-II Alignment Requirements
Cavities

Value

Transverse cavity alignment error, mm RMS
Angular cavity alignment error, mrad RMS<1≤10

Solenoids

Value

Transverse cavity alignment error, mm RMS
Angular solenoid alignment error, mrad RMS

<0.5
≤1

H-BCAMs® [2] are optical instruments first used in highenergy physics during the HIE ISOLDE experiment at
CERN [3] and later adapted for PIP-II. The H-BCAMs system has been successfully employed to monitor the alignment of SRF cavities in prototype SSR1 and HB650 CMs[4–6].
The alignment established during the assembly phase mustaccount for the movements that cavities and magnets experi∗ Work supported by Fermi Research Alliance, LLC under Contract No.

DEAC02- 07CH11359 with the United States Department of Energy,
Office of Science, Office of High Energy Physics.
† jbernard@fnal.gov
MOPB0640

Figure 1: Measurement set-up used in the STC. Three HBCAMs (a, b, and c) face the three targets (A, B, and C)
mounted on the SSR2 cavity.

MEASUREMENT SYSTEMThe STC is equipped with a pair of G-10 support posts,
which are intercepted by a liquid nitrogen-cooled thermal
shield. These support posts provide thermal insulation, keeping components at 2 K separate from those at ambient temperature. As shown in Fig. 1, one post supports the SSR2
cavity, while the other supports an aluminum stand that holds
MOPB: Monday Poster Session
MC4.2 Cryomodules and cryogenics

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INTEGRATION OF COMPUTER VISION SYSTEM TO TRACK THE
ALIGNMENT OF SRF CAVITIES INTO THE TEST CRYOSTAT FOR PIP-II
AT FERMILAB∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB065

J.P. Holzbauer† , J. Helsper, J. Ozelis, A. Wixson
Fermi National Accelerator Laboratory, Batavia, IL, USA
M. Kane, STFC-UKRI, Warrington, UK
Abstract
The PIP-II Project will receive fully assembled cryomodules from CEA and STFC-UKRI as in-kind contributions.
Damage to these cryomodules during transport is understood
to be a significant risk to the project, so an extensive testing and validation program has been executed to mitigate
this risk. The centerpiece of this effort was the successful
shipment, from FNAL to STFC-UKRI and back, of a prototype HB650 cryomodule with cold testing before and after
shipment to verify no functionality changes from shipment.
Building on an escalating test transport program, the prototype cryomodule was shipped to the UK and back using
realistic logistics, handling, instrumentation, and planning.
The process of executing this shipment, lessons learned, andplan moving forward will be presented here.

INTRODUCTION
The PIP-II SRF linac is composed of five cryomodule
types at 3 sub-harmonics of 1.3 GHz (162.5, 325, and
650 MHz) [1]. The 650 MHz section of the linac is composed of two cryomodule types, Low-Beta (LB) and HighBeta (HB). The PIP-II Project has significant international
contributions in almost every part of the machine, and the
650 section is no exception. The LB modules are being
designed and produced by CEA in France while the HB
modules are produced by STFC-UKRI in the UK as in-kind
contributions to the project. The PIP-II project has adopted
the strategy of convergent design, aligning the techniques
and technologies between different modules as much as possible. This allows convergent mitigation of the transportation
risks for the LB and HB modules from the partner labs in
Europe to FNAL. Transportation experts at all three labs
have worked closely to ensure that a consistent and systematic approach is used for assessing and mitigating the risksof these critical cryomodule transports.

TRANSPORT SYSTEM VALIDATIONSTRATEGY
The systematic approach to transportation and transport
validation has been adopted by PIP-II driven by past experience with cryomodule shipping for LCLS-II [2]. This
includes the choice to forego sea and rail, relying on airtransport for the transatlantic segments. The following major stages are chosen to systematically validate the integrated∗ Work supported by Fermi Research Alliance, LLC under Contract No.

DE-AC02-07CH11359 with the United States Department of Energy.

† jeremiah@fnal.gov

MOPB: Monday Poster Session
MC4.2 Cryomodules and cryogenics

transport system design (cryomodule plus shipping frame)
while minimizing risk to critical equipment.
1. Detailed specification, design, and review of the HB650
transport frame in collaboration between FNAL and
STFC-UKRI [3, 4]
2. Fabrication, integration of HB650 transport frame withcryomodule analog (Dummy Load), realistic testingwith Dummy Load to validate isolation and handling
performance, first locally via road and then from to
STFC-UKRI, validating air transport and handling [5,6]
3. Local road testing with a cold-tested and validated prototype HB650 (pHB650) to reverify isolation performance as well as any module-internal resonances
4. Realistic transport of the pHB650 module from FNAL
to STFC-UKRI and back, concluding with second coldtest to assess impacts of transatlantic shipment on cavity
performance [7]5. Design optimization of HB650 and LB650 transport
frames by the respective partner labs [8].
All stages of this validation effort have been completed
successfully including the cold re-validation of the cryomodule performance. This paper will describe the final shipmentof the pCM to the UK and back, including major lessons
learned.

TRANSPORT SYSTEM DESIGNThe HB650 transport system, designed by STFC-UKRI,
is a tessellated steel frame meant to enclose the cryomodule
during transport, isolating the CM during transport withwire-rope isolators sized for the weight and shocks/vibrations
expected during transport. The model of the transport system(frame, isolators, and CM) can be seen in Fig. 1. The frame
is covered in plywood panels during transport to prevent
access and protect from weather. Access ports were added toallow instrumentation inspection during transport, viewing
windows in case of customs inspections, and labeling forease of assembly.
During the fabrication, dummy load testing, and final
validation with CM, this design was fundamentally foundto be sound with minor changes proposed. These lessons
learned mostly consisted of:• Revisit and improve all connections, especially on outerpanels, which will see wear and tear of multiple shipments. The more robust these materials and attachment
points can be, the better
MOPB065
187

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SUCCESSFUL INTERNATIONAL VALIDATION TEST SHIPMENT OF THE
PIP-II HB650 CRYOMODULE TRANSPORTATION SYSTEM∗

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PERFORMANCE OF PIP-II HIGH-BETA 650 CRYOMODULE AFTER
TRANSATLANTIC SHIPPING*
J. Ozelis†, M. Barba, J. Bernardini, C. Contreras-Martinez, D. Crawford, J. Dong, V. Grzelak,
P. Hanlet, J. B. Holzbauer, Y. Jia, S. Kazakov, T. Khabiboulline, J. Makara, N. Patel, V. Patel,
L. Pei, D. Peterson, Y. Pischalnikov, D. Porwisiak, S. Ranpariya, J. Steimel, N. Solyak,
J. Subedi, A. Sukhanov, P. Varghese, T. Wallace, M. White, S. Wijethunga, Y. Xie, S. Yoon
Fermilab, Batavia, USA
Abstract
After shipment to the Daresbury Lab and return to Fermilab, the prototype HB650 cryomodule underwent another phase of 2K RF testing to ascertain any performanceissues that may have arisen from the transport of the cryomodule. While measurements taken at room temperature
after the conclusion of shipment indicated that there wereno negative impacts on cavity alignment, beamline vacuum, or cavity frequency, testing at 2K was required to validate other aspects such as tuner operation, cavity coupling,
cryogenic system integrity, and cavity performance. Results of this latest round of limited 2K testing will be presented.

INTRODUCTION
The PIP-II Superconducting Linac features 23 cryomodules of 5 different types. The highest energy section of the
Linac is comprised of 9 Low-Beta (LB) 650 MHz cryomodules with 4 cavities, and 4 High-Beta (HB) cryomodules with 6 cavities. Except for a prototype HB cryomodule, the remaining 650 MHz cryomodules (including therefurbishment of the HB650 prototype cryomodule) are to
be assembled by international partners (CEA and INFN for
LB, UKRI’s Daresbury Lab for HB) as in-kind contributions to the PIP-II project. As a result, 13 of the cryomodules to be used in the P IP-II Linac will require that they
undergo transatlantic shipment to the US.
Reducing the risk that this transatlantic shipment resultsin performance degradation or damage to these cryomodules is paramount. To that end two approaches have beentaken to understand the environmental conditions posed bysuch transport and to mitigate risks: Shipment of a fully instrumented “dummy load” toperform preliminary verification of shipment methods and transport fixtures
 Shipment of the prototype HB650 cryomodule(HB650 pCM) to Daresbury Lab after completion of
2K testing at Fermilab’s PIP2IT facility, and re-test
upon return
Shipment of the dummy load was performed during
summer 2022. As reported elsewhere [1], the results indicated that the fixturing and processes (adopted from similar____________________________________________* This manuscript has been authored by Fermi Research Alliance, LLC
under Contract No. DE-AC02-07CH11359 with the U.S. Department ofEnergy, Office of Science, Office of High Energy Physics.
† ozelis@fnal.gov
MOPB067190

experience shipping LCLS-II cryomodules from FNAL to
SLAC) worked extremely well, and minor changes were
pursued to incorporate lessons learned. y
The shipment of the actual pCM took place late in 2023,
after the first round of RF testing of the cryomodule at 2K
to characterize initial performance was completed in the
PIP2IT facility at Fermilab. The shipment configuration,
preparation, and process for shipment of the completed
HB650 pCM is described in detail in [2].

TRANSPORT-CRITICAL CRYOMODULEPERFORMANCE PARAMETERS
A number of critical performance parameters or system/component functionalities were the primary focus of
the post-transport study. These include :











Insulating vacuum integrity
Beamline vacuum integrity
Cryogenic circuit integrity
Cavity alignment preservation
Tuner operation
Cryogenic valve actuator operations
Instrumentation
High-power coupler Qext
Cavity performance (gradient, field emission, andquality factor)
Thermal performance consistency

Each of these areas were subject to test/measurement,
and results to be compared with performance observed before shipment.

TEST APPROACH AND PLAN
Upon return from the UK, the HB650 pCM was partiallyre-assembled, as the top port and its internal components(e.g., heat exchanger, thermal and magnetic shields) andpower coupler air-side components were removed fortransport. This re-assembly activity also provided an opportunity to make several modifications to the cryomodule
cryogenic systems and mechanical structure, based on results and analysis from earlier thermal studies. A checkvalve was installed in the 2K relief line, additional MLI
was added, and temperature sensors and heaters were installed on the cryogenic valve thermal intercepts, to bettercharacterize heat transfer and examine the possibility ofthermo-acoustic oscillations [3].
MOPB: Monday Poster Session
MC4.2 Cryomodules and cryogenics

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HIGH PRESSURE RINSE SIMULATIONS FOR PIP-II SRF CAVITIES∗
M. Parise† , T. Aiazzi, D. Passarelli
Fermi National Accelerator Laboratory (Fermilab), Batavia, IL, USA
Abstract
The implementation of High Pressure Rinse (HPR) not
only ensures thorough cleaning of the inner high purity niobium surface of Superconducting Radio Frequency (SRF)
cavities, but also unlocks their full potential for achieving
peak performance. By effectively removing contaminants
and impurities, HPR sets the stage for enhanced superconducting properties, improved energy efficiency, and superior
operational stability. A simulation tool has been developed,
facilitating the accurate prediction of both the quality andeffectiveness of the rinsing process before its execution in
the cleanroom. This tool, the focus of this paper, stands as apivotal advancement in optimizing Superconducting Radio
Frequency (SRF) cavity preparation. Furthermore, our paper
will also present correlations with cavity cold testing results,
demonstrating the practical applicability and reliability ofthe simulation predictions in real-world scenarios.

INTRODUCTION
The performance of Superconducting Radio Frequency(SRF) cavities showcases the state-of-the-art of what we canachieve with today’s technology. As we push the boundaries of particle acceleration, the fabrication and processingof these cavities emerge as critical factors that determine
their performance. This is particularly true for non-ellipticalcavities, whose intricate geometries present additional challenges. Unlike the Tesla-shaped cavities, for which standard
processes have been refined and optimized over time, nonelliptical cavities demand a reevaluation of existing methodologies. Their complex shapes not only necessitate advanced
manufacturing techniques but also call for innovative processing solutions to ensure optimal performance. Field Emission (FE) issues have been a persistent bottleneck during
the cold testing phase of jacketed Single Spoke Resonators
Type 2 (SSR2) ( [1], [2], [3], [4]) for PIP-II (PIP-II [5]) ,where the presence of particulate contaminants has severely
impaired the cavity’s functionality. This paper investigatesthe cleaning of SSR2 cavities. The motivation behind thisstudy stems from the difficulties in achieving an effective
high-pressure rinse. Due to the cavities’ convoluted geometry, standard water jet cleaning procedures fail to reach, or
effectively clean, all surfaces. This inadequacy is attributed
to the limitations in water jet coverage and the dynamics of
fluid interaction with the cavity walls. The efficiency of therinse is contingent upon several factors: the angle between
the water jet and the cavity surface, the duration for which
specific areas are subjected to the high-pressure water, andthe distance from the nozzle to the surface at the point of∗ Work supported by Fermi Research Alliance, LLC under Contract No.

DE-AC02-07CH11359 with the United States Department of Energy† mparise@fnal.gov

MOPB070194

impact. It is hypothesized that the angle of incidence playsa pivotal role in the cleaning process, where certain angles
may enhance the rinse effectiveness, while others may leadto suboptimal results. Similarly, the time of exposure andthe distance of the water jet from the surface are criticalparameters that determine the force exerted by the water jet,and consequently, its cleaning efficacy. In the context of thiswork a new tool to simulate the HPR cavity surface coverage,
effeciency, time of exposure and nozzle to surface distancehas been developed (see also [6], [7]). Additionally, The
code has been meticulously crafted to significantly reduce
computational time. This efficiency enables the execution of
optimization processes that would otherwise be impracticaldue to their iterative nature. By minimizing the time required
for each run, the code facilitates a level of optimization thatwas previously unattainable. By fine-tuning the angles atwhich the high-pressure water strikes the cavity surfaces, we
can significantly enhance the rinse, ensuring that all areas
are effectively reached and contaminants are removed. This
leads to a direct improvement in the performance of the cavities by mitigating field emission issues, which is a criticalstep forward in the maintenance and operation of advanced
particle accelerators.

DEVELOPMENT OF THE
SIMULATION TOOL
Process Description and Input Parameters
The HPR process is performed in a controlled cleanroom
environment to ensure the performance of SRF cavities.
Central to this process is a wand equipped with a series ofnozzles, typically ranging from 2 to 8, through which highpressure water is directed onto the cavity surfaces. These
nozzles, often sourced from commercial vendors, are designed to spray water at specific angles referred to as thewater jet angle. To accommodate the varying geometries of
SRF cavities, the nozzles can be oriented at different angles.
This parameter, which could be termed as the nozzle orientation angle, is crucial for optimizing the cleaning coverage.
These angles are the azimuthal and polar angles. Also nozzles may be spaced at a certain distance along the wand axis.
Although this distance is small compared with the dimensionof the cavity it is included in the model. The wand itself
is engaged in a relative motion with the cavity, which may
involve rotation and translation at certain speeds to ensurecomprehensive cleaning. Although the cavity itself may
rotate and translate, it is the relative motion between the twothat is of importance. Low beta cavities, such as the SSR2
cavities with their four ports, present unique challenges dueto their complex geometry. In our simulations, the wandis positioned vertically or slightly tilted with respect to the
MOPB: Monday Poster Session
MC4.8 Superconducting RF

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PLANNED FUTURE UPGRADES OF LINEAR IFMIF PROTOTYPE
ACELERATOR (LIPAc)
F. Cismondi, D. Duglue, H. Dzitko, A. Jokinen, F. Scantamburlo, F4E, Garching, Germany
T. Akagi, Y. Carin, D. Gex, K. Masuda, I. Moya, M. Sugimoto, IFMIF/EVEDA Project Team,
Rokkasho, JapanK. Hasegawa, K. Hirosawa, K. Kondo, K. Kumagai, QST, Rokkasho, Japan
P. González, ATG, Barcelona, Spain
IFMIF/EVEDA Integrated Team with CEA, CIEMAT, INFN, Italy
Abstract
The Implementing Agencies of the Broader Approach(BA) agreement, namely Fusion for Energy (F4E) andNational Institutes for Quantum Science and Technology(QST), are developing the Accelerator Facility validation
activities that aim at demonstrating the acceleration of
125 mA D+ beam up to 9 MeV in continuous wave (CW)[1,2]. This is the main goal of the Linear IFMIF Prototype
Accelerator (LIPAc) under installation, commissioning andoperation in Rokkasho, Japan.
LIPAc has been operated until June 2024 in its Phase B+
configuration, which consists of all the beamline except the
SRF Linac (high duty cycle operation results up to 5 MeV
are reported by T. Akagi in this conference).
In parallel, the upgrades for several systems are being
designed and procured taking into account the lessons
learned so far during commissioning and operation andwill be the main object of this paper. These systems are: a
new injector encompassing a new design of beam
production and extraction system together with LEBT; anew RF system based on SSPA technology for the RFRFQ, whose full-scale prototype is being manufactured
and validated in 2024; a new set of RF-RFQ power
couplers with improved design to overcome the limitations
suffered by the couplers currently installed in LIPAc.

INTRODUCTION
The LIPAc [1, 2] in its Phase B+ configuration consistsof a 100 keV injector, a 5 MeV Radio-Frequency
Quadrupole (RFQ) accelerator, a Medium and HighEnergy Beam Transport lines (MEBT and HEBT
respectively) and a Beam Dump (BD). Its final
configuration will include a Superconducting RadioFrequency (SRF) Linac and will target to commission abeam in CW of 125 mA at 9 MeV. A temporary MEBT
Extension Line (MEL) replaced the SRF linac during
Phase B+.
The beam generated at the ion source has an emittance
below 0.3π.mm.mrad at the entrance of RFQ. The LIPAc
commissioning is currently on-going at Rokkasho Institutefor Fusion Energy [3]. In 2019 the beam commissioning
campaigns achieved RFQ acceleration at nominal current
125 mA, 5 MeV at low duty cycle (DC) of ~0.1 % (1mspulse) [4, 5]. Since the installation of the HEBT and the DP
in 2020 and 2021, a deuteron beam of around 20 mA at

MOPB071198

0.01 % duty cycle was transported up to the High-PowerBeam Dump in December 2021 [6, 7].

ENHANCED INJECTOR
The LIPAc Injector CW commissioning campaigns havebeen conducted with ɸ9, ɸ10, ɸ11, and ɸ12 mm plasma
electrodes (PE) apertures. By using the ɸ11 mm PE, a total
current of 150 mA was extracted in CW (11 hours
continuous operation) with D+ fraction of 91% (D+ = 137mA), and a low emittance (0.24 π mm mrad). Also, byusing a ɸ12 mm PE, CW operation and a total current of
160 mA were achieved, but the emittance increased to 0.3
π mm mrad and the beam current stability deteriorated. The
ɸ11.5 mm is considered the optimum electrode diameterfor stable extraction of the target CW current [8, 9], andwas used during the Phase B+.

General Layout and Design Features
The upgrade of the Injector (see Fig. 1) should
encompass studies of the current CW campaigns and thebeam operation results to identify the best design options
for the injector subparts. It is likely that the most importantefforts and changes will target to upgrade the accelerator
column and the Emittance Meter Unit (EMU). The efforts
will nevertheless not be limited to optimize thosecomponents, but rather to design a full upgraded injector.
For the EMU, the development of an optimized design
target to improve its overall performance. It is very
important for LIPAc to study the possibility to perform
emittance measurements up to at least 10%DC. The
optimized design can be based on the improvement of thecooling system, the better choice of the materials tomaximize the heat dissipation and minimize deformations,an upgrade of its LCS, and the improvement of the
manufacturing. The upgrade of the accelerator column will
target to improve the overall performance in particular thestability at high duty cycle and continuous wave operation
modes. Elements to take into account for the design
upgrade are the optimization of the distance between theelectrodes, the profiles of the electrodes, the improvementof the behaviour against the voltage breakdown, theoptmization of the magnetic field into the plasma chamber,the magnetic shielding between the plasma chamber andthe electrodes, and the capability to check the electrodes
mechanical alignment.
During the LIPAc injector campaigns a quicker than
expected degradation of the Boron Nitride (BN) disk was
MOPB: Monday Poster Session
MC3.2 Ion linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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J. Peng1,2, †, Y.L. Han1,2, Z.P. Li1,2, Y. Li1,2, Y. Yuan1,2, X.Y. Feng1,2, M.Y. Huang1,2, S. Wang1,2,
S.N. Fu1,2, H. Liu1,2
1
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
2
Spallation Neutron Source Science Center, Dongguan, China
Abstract
The transverse emittance at the exit of the China Spallation Neutron Source（CSNS）DTL is measured regularly
every year. However, recently, the measured transverse
emittance growth became larger than the historical data. It
is also bigger than the simulated emittance. The process ofmeasurement, data analysis and matching methods used
are almost the same. Several factors contributed to thetransverse emittance growth are analysed and presented inthis paper. Compared to other factors, longitudinal mismatch contributes the most growth.

INTRODUCTION

25%, the activation levels throughout the linac didn’t increase. It kept less than 7mrem/hour at 30cm. And thebeam profile obtained from the wire scanner measurement
at the exit of the DTL also didn’t show any significant
beam halo, indicating that the beam didn’t mismatch seriously.
Table 1: Main Parameters of the CSNS Linac
Ion Source RFQ DTL
Input Energy (MeV)
0.05
3.0
Output Energy (MeV)
0.05
3.0
80
Pulse Current (mA)20
10
10
RF frequency (MHz)324
324
Chop rate (%)
50
50
Duty factor (%)
1.3
1.05 1.05
Repetition rate (Hz)25
25
25
Several factors contributing to transverse emittance
growth are analysed, including mismatch and imcomplete
transverse lattice. We also performed beam experiments toslove these issues.

EMITTANCE GROWTH STUDIES
Figure 1: CSNS linac layout.
The CSNS is designed to accelerate proton beam pulse
to 1.6GeV at a 25Hz repetition rate while striking a solid
metal target to produce spallation neutrons. The accelerator
aims to provide 100kW of proton beam power with morethan 90% reliability. In 2024, the beam power is increased
to 160kW with more than 93% reliability. The accelerator
complex consists of an 80MeV H- linac as the injector anda 1.6GeV rapid cycling proton synchrotron (RCS), as
shown in Fig. 1 [1]. The linac consists of a 50keV H- ionsource, a 3MeV RFQ, an 80MeV DTL, and several beamtransport lines. Table 1 shows the main parameters of the
CSNS linac.
The transvers beam emittance at the exit of the DTL is
measured regularly. However, this year, the transverse
beam emittance increase about 25% compared to the recorded value. In 2021, the horizontal and vertical rms emittance is 0.346 and 0.337 πmm mrad at the beam currentof 15mA. For this year, the horizontal and vertical rms
emittance is 0.434 and 0.399 πmm mrad at the same current. Although the transverse rms emittance growed about

Mismatch
Discrepancies between the physical model and actualmachine parameters are common, and these differences
can typically be minimized using beam-based calibration
methods [2]. The CSNS MEBT consists of ten quadrupoles
and two buncheres, which are utilized for longitudinal andtransverse matching. The equivalent slicing model method
is employed to construct magnet models [3], incorporating
the fringing field effect. The amplitude and phase of two
bunchers are determined using the phase scan signature
method [4]. A pair of FCTs after each buncher is used tomeasure the beam phase difference during cavity amplitude and phase scanning. By matching the measured beamphase difference to the simulated beam phase differences,the cavity phase and amplitude can be determined. However, as the pair of FCTs is close to the buncher and thevoltage of the buncher is small compared to an accelerating
cavity, results in insufficient precision of the amplitude calibration. Discrepancies between the amplitude from thematching calculation and the actual RF setting can lead totransverse emittance growth.

____________________________________________* Work supported by National Natural Science Foundation of China(11505201)† pengjun@ihep.ac.cn
MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

MOPB073
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STUDIES OF TRANSVERSE EMITTANCE GROWTH
IN CSNS LINAC DTL*

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PROGRESS IN THE DEVELOPMENT OF THE CRYOMODULES FOR
CSNS-II SUPERCONDUCTING LINAC
M. Xu†, R. Ge, M. Li, Z. Chang, K. Zhu, J. Zhou, Y. Han, W. Zhou, Z. Mi,
F. He, Z. He
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
Abstract
The China Spallation Neutron Source phase II (CSNSII) upgrade design will increase the total beam power from100 kW to 500 kW and boost the beam energy from80 MeV to 300 MeV in the linac by adding a
superconducting linear accelerator to the existing
accelerator complex. Its proton linac will include
18 superconducting cavity cryomodules. It is composed of
one string of Spoke cavity cryomodule and another stringof elliptical cavity cryomodule. The nominal operating
temperature for the cavities is 2 K, with 50~60 K thermal
shielding. This paper introduces the thermo-mechanicaldesign and expected operation of the CSNS-II spoke cavity
cryomodule and elliptical cavity cryomodule, it also
include the horizontal test results about the prototype of
Spoke cavity cryomodule with two cavities.

INTRODUCTION
The China Spallation Neutron Source (CSNS) is the first
pulsed neutron source facility in developing countries.
CSNS locates at Dalang Town of Dongguan City, the heartof the Guangdong-Hong Kong- Macao Greater Bay Area.
The China Spallation Neutron Source phase II (CSNS-II)
upgrade design will increase the total beam power from100 kW to 500 kW and boost the beam energy from80 MeV to 300 MeV in the linac by adding a
superconducting linear accelerator to the existing
accelerator complex. Based on superconducting
radiofrequency technologies, the superconductign linear
accelerator will operate for the first time a 90 meter longsection of niobium cavities.
It is composed of 10 Spoke cavity cryomodules and
8 elliptical cavity cryomodules. Paired in 18 cryomodules,
each cavity will generate an accelerating pulsed field of
9MV/m. The cryogenic system is the specialised techicalsystems and can be further divided into two subsysytems:
the linac cryoplant and the test stand and instruments
cryoplant. The linac cryoplant will provide all the coolingto the 18 cryomodules containing the superconducting RF
cavities. The PID design of the linac cryoplant is finished.
The test stand and instruments cryoplant have been
finished commissioning and under nomal operation for
more than 3 years.
A prototype of double Spoke cavity cryomodule housing
two superconducting Spoke cavities and their RF power
couplers is now being fabricated and assembled. It
provides the cryogenic environment for their normal
operation in a 2K saturated superfluid helium bath: a 60 K
thermal shield, a cold magnetic shield enclosed cavities,
and integrates all the interfaces necessary to be operational
MOPB077
204

within the linac machine. This prototype has finished thecryogenic horizontal test at Platform of Advanced Photon
Source Technology R&D (PAPS) site and then it isprepaired to transport to CSNS site.

LINAC CRYOPLANT
The linac cryoplant provides cooling at three nominal
temperature levels : 45 K to 60 K for the thermal shields ofthe cryomodules, valve boxes, 60 K thermal intercepts ofthe power coupler and beam pipe and distribution system;
5 K for the power coupler thermal intercepts and 2 K for
the SRF cavities. The linace consists of 18 cryomodules
operating at 324 MHz for the Spoke cavities and 648 MHz
for the elliptical cavities. The CSNS-II cryomodules areindividual cryogenic units and are cooled in parallel by thecryogenic distribution system. Figure 1 is a flow schematic
fo the helium distribution system of superconducting linac.
Figure 2 shows the layout of the superconducting linac.

Figure 1: Flow schematic fo the helium distribution system
of CSNS-II superconducting linac.

Figure 2: The layout of the superconducting linac.

MECHANICAL DESIGN
The superconducting linac of CSNS-II includes two typeof cyomodules, one is Spoke cavity cryomodule andanother is elliptical cavity cryomodule. A cut view of the
Spoke cavity cryomodule is shown on Fig. 3. The two
double Spoke cavities are installed along the axis of thevacuum vessel. Cold tuning systems are vertical mounted
at the side of helium bath of cavity, which face toward theend head assembly of the vacuum house to facilitate themaintenance operations. Cold magnetic shields cover the
helium bath of cavity. The RF power couplers arehorizontal installed and its thermal anchors are connectedto the corresponding cold source by copper braided tapes.
The bi-phase pipe is positioned horizontally on the top of
the cavities. The cold mass is surrounded by the thermal
shield.

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MC4.2 Cryomodules and cryogenics

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NEUTRALIZER-BASED LONGITUDINAL BUNCH PROFILEMEASUREMENT DESIGN*
C.E. Taylor†, H. Andrews, E.C. Huang, J.W. Lewellen, C. Rohde, R.T. Thornton
Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Abstract
The Longitudinal Profile Monitor (LPM) system aims tomeasure and control particle beam tails in high-power particle accelerators. Using a picosecond laser, portions of Hion beams are neutralized into H0 atoms for detection. Despite challenges in laser synchronization and hardware installation, progress was made in laser system development,
beamline hardware installation, and magnet system integration. This project advances diagnostic technology andworkforce development, positioning LANL at the forefrontof H- beam diagnostics. Continued programmatic efforts
will focus on overcoming remaining challenges and completing the development of this diagnostic tool.

BACKGROUND AND OBJECTIVES
The primary objective of this project was to develop a
non-perturbative diagnostic tool capable of accurately
measuring the longitudinal profile of H- ion beams within
accelerators. Traditional diagnostic methods often requireintercepting the beam, which can be disruptive to the accelerator’s operation [3]. Our approach was different. We
proposed using a picosecond (ps) laser to selectively neutralize portions of the beam, converting H- ions into neutral
Ho atoms (Fig. 1). This process allows for the measurementof the beam’s profile without significantly disrupting thebeam’s operation, making it a transformative advancement
over existing diagnostics.

INTRODUCTION
The neutralizer-based LPM project has been a pivotal
endeavor in advancing the field of particle accelerator diagnostics. This project, initiated to tackle the challenges associated with measuring and controlling the tails or halosof high-power particle beams, has involved intricate planning, extensive collaboration, and the integration of cutting-edge technology [1, 2]. As we reach a critical juncturein the project’s timeline, it is essential to reflect on the journey so far, the technical progress made, the challenges encountered, and the outcomes achieved. Here, we provide acomprehensive overview of the project’s development,
highlighting key milestones and setting the stage for futureadvancements.
Particle accelerators like those at the Los Alamos Neutron Science Center (LANSCE) and the Spallation Neutron
Source (SNS) are essential tools in both scientific researchand national security missions. These accelerators generate
high-energy beams of particles that are used in a variety of
applications, from fundamental physics research to themaintenance of the national nuclear stockpile. However,
one of the persistent challenges in operating these accelerators is the presence of beam tails or halos—portions of thebeam that contain only a small fraction of the total beam
current but can have significant consequences if notproperly managed. Even small beam losses can lead to radiation generation, component activation, and physicaldamage to the accelerator itself. Thus, developing a reliable method to measure and control these tails is of paramount importance.

___________________________________________* This work benefitted from the use of the LANSCE accelerator facility.
Work was performed under the auspices of the US Department of Energy
by Triad National Security under contract 89233218CNA000001.
† cetaylor@lanl.gov
MOPB080
208

Figure 1: Schematic of the diagnostic.
The project was designed with several specific technicalgoals in mind:
1. Measurement of self-neutralization rates: Understanding how H- ions naturally convert to neutral atoms within the accelerator. Initially, this was considered critical for calibrating the diagnostic tool. However, it was later determined that collecting thestripped electrons would provide the necessary data
without requiring the measurement of self-neutralization rates.
2. Measurement of the longitudinal bunch profile:Achieving a resolution of approximately 1 ps was essential for capturing the fine details of the beam structure. This high resolution would allow us to measure
the bunch length and tail amplitude with unprecedented precision.
3. Detection of shadow bunch amplitudes and profiles: Beam tails extending to at least 4σ from thebunch center were of particular interest. By accurately
measuring these tails, we could minimize radiation
production and optimize the beam transport process.
MOPB: Monday Poster Session
MC4.1 Beam diagnostics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISSN: 2226-0366

doi: 10.18429/JACoW-LINAC2024-MOPB081

GENERALIZATION ABILITY OF CONVOLUTIONAL NEURALNETWORKS TRAINED FOR COHERENT SYNCHROTRON RADIATIONCOMPUTATIONS ∗C. Leon† , P.M. Anisimov, N. Yampolsky, A. Scheinker
Applied Electrodynamics Group, Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract
Coherent synchrotron radiation (CSR) has a significant
impact on electron storage rings and bunch compressors,
inducing energy spread and emittance growth in a bunch.
Calculating the effects of CSR is computationally expensive,
severally limiting the use of simulations. Here, we explore
utilizing neural networks (NNs) to model the 3D wakefields
of electrons in circular orbit in the steady state condition.
NN models were trained on both Gaussian and more generalbunch distributions, which evaluate much faster than physicsbased simulations. Here, we explore how well the models
generalize, by testing their ability to: 1) extrapolate to Gaussians with smaller/larger widths 2) predict on distributions
never encountered before (out of distribution generalization)using smoothed uniform cubes. We see the models are able
to generalize, which makes them potentially useful in the design and optimization of accelerator apparatuses by enabling
rapid searches through parameter space.

INTRODUCTION
Coherent Synchrotron Radiation (CSR) can significantly
alter the distribution of electrons moving in circular orbit,
such as in an electron storage ring or a bunch compressor.
For emitted wavelengths, 𝜆, much larger than the bunchsize, then at 𝜆-resolution the bunch looks point-like, and the
𝑁𝑒 electrons look like they’re all undergoing nearly identical motion. Consequentially, the radiation emitted by theseelectrons are approximately in phase and adds up coherently, resulting in an intensity of 𝒪(𝑁𝑒2 ). This can significantly distort the bunch phase space distribution. In theultra-relativistic limit, this primarily causes the tail and center of the bunch to lose energy while the head gains, leading
to an increase in emittance.
The electromagnetic (EM) field produced by a charged
point particle in motion is given by the well-known LiénardWiechart (LW) fields [1–3]:
E=

𝑞
n−𝛽
n × (n − 𝛽) × 𝛽)̇
(+)∣ ,4𝜋𝜖0 𝛾2 (1 − n ⋅ 𝛽)3 𝜌2𝑐(1 − n ⋅ 𝛽)3 𝜌
𝑟𝑒𝑡.
(1)

1
n × E,(2)𝑐
where the 𝑟𝑒𝑡. signifies that the expression must be evaluatedat the retarded time to ensure causality.
B=∗ Work was supported by the Los Alamos National Laboratory Laboratory

Directed Research and Development (LDRD) DR project 20220074DR.

† cleon@lanl.gov

MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

The total force an electron experiences due to the radiation
emitted by other electrons in the past is called the wakefield,
W(r, 𝑡). To find it, one must integrate the Lorentz force,
F(r, 𝑡), generated by the LW fields in Eqs. (1) and (2) along
the past light cone:W(r) = ∫ 𝑑 3 r ′ 𝜆(r′ , 𝑡 ′ )F(r ′ , 𝑡 ′ )∣
△

𝑟𝑒𝑡.

,

(3)

where △ signifies the past light cone, time in the integrandis the retarded time and 𝜆(r ′ , 𝑡 ′ ) is the number density. The
computational storage needed to do the evaluations at theretarded times and the computational expense of 𝒪(𝑁𝑒2 )interactions, with typical bunch sizes of 𝑁𝑒 ∼ 1010 , foreach time step makes designing practical software for CSR
calculations a formidable task. To deal with the complexities,
many approximations are commonly used, such as the 1D
approximation [4]. Even in the specific case of circularmotion in the 1D approximation, though, the incorporationof CSR effects in a simulation can increase the running
time of the simulation by an order of magnitude [5]. This
makes many conventional simulations far too slow for some
applications, such as a thorough exploration of parameter
space to optimize accelerator component design. With the
production of smaller bunch sizes in accelerator facilities,
the need for a fast and accurate account of 3D CSR has
become important.
Machine learning (ML) can speed up simulations to provide real-time virtual diagnostics which can be used forreal-time adaptive beam control. For example, in [6] thefirst approach to adaptive ML was demonstrated combining
a deep learning with adaptive feedback [7] for automatic
control of the longitudinal phase space of the LCLS FELelectron beam. They can also be used to speed up accelerator simulations [8, 9]. Convolutional neural network (CNN)
computations utilize matrix multiplications and several parallelized operations and with modern GPU’s, which are
optimized for such tasks, can be performed rapidly. Hence,a CNN trained on CSR simulations data can lead to very fastcomputations.
Previous work has investigated the use of ML surrogate
models to speed up CSR calculations. Mayes and Edelen
used a dense neural network in the 1D case to speed up CSR
calculations [10]. CNN’s in particular have been utilized in
the 2D transient case [11].
Here, we take previous CNN models trained to predict
the fully 3D wakefields generated by electrons at steadystate [12] and see their generalization ability. Specifically,
we investigate at how well it performs at extrapolating to
MOPB081
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ISBN: 978-3-95450-219-6

JACoW Publishing32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB082

C.-M. Alvinerie†, E.-C. Huang, S. Sosa Guitron, C. Taylor, J. Upadhyay
Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Abstract
At the Los Alamos National Neutron Science Center(LANSCE), the LANSCE Modernization Project (LAMP)
includes beamline studies that could help the operation. For
the PSR, reducing or at least controlling the beam losses
could maximize the beam current delivered to the users andextend the run cycle via shortening the maintenance period.
One of the approaches would be to install collimations thatare not present at LANSCE. Preliminary results are discussed in this proceeding to evaluate various possibilities
of collimation systems along the high energy beamtransport and/or in the ring.

INTRODUCTION
The Los Alamos Neutron Science Center, illustrated inFig. 1, is a unique facility with several applications for engineering and science studies. In this facility, the Drift Tube
Linac and the Side Coupled-Cavity Linac accelerates a Hbeam up to 800 MeV to deliver it to multiple user stations
requiring different beam structures.
In this configuration, the Proton Storage Ring (PSR)
compresses a long macro pulse of protons (625 µs) at anominal 800 MeV energy into a short pulse of 290 ns. Thisempowers the Manuel Lujan Neutron Scattering Center forexperiments using spallation neutrons. Facility users would
prefer a higher beam current for a better signal-to-noise ratio. However, this current is limited by the beam losses,
among other reasons.

Figure 1: Overview of the LANSCE facility [1].
Radiations produced by beam losses require long cooldown time and prevent hands-on maintenance after the
beam production period. Reducing beam losses will produce less radiation in the PSR and potentially shorten themaintenance time required. Furthermore, the beam inside
the ring can be imperfect due to instabilities like the electron-proton instability [2]. This instability describes the___________________________________________† calvinerie@lanl.gov

MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transportinteraction between an electron cloud potentially produced
from lost particles and the subsequent proton bunches.
Therefore, it could be reduced by at least controlling thebeam losses.
Prospective studies are explored to reduce or at least
controlling the beam losses in the PSR. One of the solutions would be to install collimation systems, not currently
present at LANSCE. For several years, beam collimation
systems are a scientific subject in different high-energy facilities (accelerators and/or rings) as at SNS [3], Fermilab[4], J-PARC [5], LHC [6] and PIP-II [7]. This proceeding
presents a study for potential locations of collimation systems at LANSCE to control beam losses. First, we introduce collimation systems that could be applied at
LANSCE. Then, we will discuss on the collimation choicefor the LANSCE facility. Finally, we will briefly propose abeam collimation experiment.

BEAM COLLIMATIONThe collimation systems are chosen depending on several factors, such as beam characteristics (species, energy),
type of collimation to be operated (off-momentum, etc.) or
location of collimators in the accelerator and/or ring.
At LANSCE, beam losses appear notably from downstream the linac to the PSR. This facility works in a similar
way as the SNS facility. So, based on collimator systems
locations at SNS, two different collimation possibilities are
discussed: around the stripping foil in PSR and/or downstream the linac (Switchyard and Line D-North areas).
The first solution could be a collimation system aroundthe stripping foil in the PSR. The idea is to install a collimator after the stripping foil and capture the partiallystripped particles and send them to the beam stop. To avoid
a full collimator due to space constraints, detail studies areundergoing to identify optimal collimation scheme. This
will not be included in this proceeding.
The second solution, around the Switchyard and Line DNorth areas, is then presented more in details. Downstream
the linac, the beam is composed of H- particles. Among all
the different collimation systems, collimation with stripping foils is particularly efficient for H- beam [8-10]. It
represents a simple mechanism to remove the beam halo,
an important source of beam losses in the ring. By using
stripping foils, the H- halo particles are converted in H+
ones, creating a different trajectory from the main bunches.
There are two ways to deal with the H+ beam: absorbing
them locally by a collimator (absorbers) or transport them
to a beam dump. In this case, the H+ beam (stripped particles) is separated from the H- beam (unstripped particles)
thanks to a magnetic field and transported to a wellshielded beam dump. Having only one beam dump for the
stripped particles instead of having a full collimator system
inside the line has a better efficiency and the advantage to
MOPB082
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COLLIMATIONS SYSTEMS STUDIES AT LANSCE

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB083

D. V. Gorelov†, D. A. Dimitrov, L. D. Duffy, E. Henestroza, S. S. Kurennoy, S. I. Sosa
Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract
LANSCE accelerator complex was successfully supporting nuclear science research at LANL for more than 50
years. However, the need of the upgrade of the linear accelerator becomes immanent due to development of themodern accelerator technology, and due to inevitable agingof the existing equipment. The first stage of the planned
upgrade of the linear accelerator at LANSCE includes thereplacement of the outdated proton and H- Cockroft-Walton (CW) sources with the modern RFQ accelerator, anddevelopment of the new DTL. The proposed DTL is designed to accelerate protons and H- ions simultaneously,
just as the existing accelerator, from 3 MeV – the output
energy of the RFQ, to 100 MeV, that will allow us to keep
existing Coupled Cavities Linac (CCL) intact. Presently
existing megawatt-class RF power amplifiers will be usedin the proposed new DTL. The details of the proposed design of the DTL will be given in the present paper. The details will include the main linear accelerator parameters,
like synchrotron and betatron oscillations frequencies, aswell as the developed techniques for the design studies.

without the drawbacks of the electrostatic magnets scheme,that is used in the existing DTL at LANSCE.
We start the design process with choosing of the suitablesynchrotron and betatron oscillation frequencies along the
DTL by finding adequate transverse focusing period lengthand PMQs strength, that can be achieved in practice. The
focusing lattice F0D0 was found to satisfy our requirements for the beam dynamics, where “0” represent empty
drift tubes, and “F” and “D” – focusing and defocusing
quadrupole in horizontal transverse plane respectively. The
result of our choice is presented in Figs. 1 and 2. The nomenclature of the variables correspond to Refs. [1,2].

INTRODUCTIONLANSCE accelerator modernization project (LAMP) is
the first stage of the upgrade of the linear accelerator facility at Los Alamos National Laboratory (LANL). This project proposes replacement of the existing CW ion sources
for protons and H- with new Low Energy Beam Transport(LEBT) at 100 keV, a new RFQ accelerator, and new Medium Energy Beam Transport (MEBT) at 3 MeV. A new
DTL will be designed to accelerate beams up to 100 MeV.

Figure 1: Synchrotron oscillations phase advance per focusing period for negligible beam current and for the design beam current of 35 mA.

SCOPING STUDIES PRINCIPLES
The main limitations of the DTL design are the existing
RF power amplifiers at frequency 201.25 MHz and maximum power ~2 MW each. We have 6 of those tubes, called
Diacrodes, and hence we are planning to have 6 accelerating DTL tanks with rf power requirements below 2 MWeach.
The other hard limitation is the existing tunnel, that the
new DTL will be placed in. The total length of the tunnel
and the available RF power dictate the range of the accelerating gradient values, that can be used in the new DTL.
We are planning to use Permanent Magnet Quadrupoles(PMQ) magnets for transverse focusing in the drift tubes,
since the available technologies give us the desired results___________________________________________* This work benefited from the use of the LANSCE accelerator facility.
Work was performed under the auspices of the US Department of Energy
by Triad National Security under contract 89233218CNA000001.
† gorelov@lanl.gov

MOPB: Monday Poster Session
MC3.4 Proton linac projects

Figure 2: Betatron oscillations phase advance per focusing
period for negligible beam current and for the design beam
current of 35 mA.
The presented combination of the phase advances avoids
the dangerous parametric resonance anywhere along theDTL, as well as stay below 90⁰, which is the limit of stableregion for beam with high current [3]. Sufficient adiabatic
continuity of the oscillation frequencies was preserved and

MOPB083
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DTL STUDIES FOR THE LANSCE FUTURE
FRONT-END UPGRADE AT LANL*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB084

E.-C. Huang†, P. M. Anisimov, A. J. Braido, M. J. Kay, L. J. Rybarcyk‡, J. K. K. Quemuel
Los Alamos National Laboratory, Los Alamos, NM, USA‡also at COMPA Industries Inc., Los Alamos, NM, USA
Abstract
The accelerator at the Los Alamos Neutron Science
Center (LANSCE) delivers beam to five user facilities,
including the Isotope Production Facility (IPF), the proton
Radiography (pRad), Ultra-Cold Neutron (UCN), Lujan
Center and the Weapon Neutron Research (WNR). The
high-power operation of the LANSCE accelerator is often
limited by the level of beam losses, especially for IPF andthe Lujan Center which require higher average current.
Longitudinal halos and tails, one of the major source beamlosses, could be easily generated via longitudinal mismatchunder present bunching scheme and the large uncertainties
of cavity power measurements. We present a GUI with an
online multi-particle model based on HPSim. This could
potentially help the beam physicists intuitively determine
the quality of the longitudinal capture after each phasescan, and therefore, reduce the beam losses due tolongitudinal mismatch.

INTRODUCTION
The acceleration and bunching scheme of the LANSCE
linac contains the following steps (Fig. 1): Both H+ and HDC beams are accelerated by their respective Cockcroft–
Walton (CW) generator to 750 keV. An H- beam chopper
creates the desired timing structure for different user
facilities, and the WNR beam goes through an additional
low-frequency buncher [1]. Afterwards, both species arebunched by their respective Pre-Buncher (PB) before
entering a common Main Buncher (MB). The buncherstransform the DC beam into the basic 201.25-MHz microbunch structures before the beam enters the Drift Tube
Linac (DTL). During operation, around 20-30% of thebeam falls outside of the DTL longitudinal acceptance andis lost in the DTL. Furthermore, since the beam fills almost
the whole phase range of the initial DTL acceleration
bucket, halos and tails could easily form from alongitudinal mismatch in the subsequent accelerating
modules in both DTL and the 805-MHz Side-Coupled
Cavity Linac (CCL).
To clean up the tails and halos generated by thelongitudinal mismatch, it normally takes operators 1-2
weeks to fully ramp up the current and lower the beamlosses to acceptable range every year after the initialphysics tune-up. Empirically, the first three of the four DTL
modules were adjusted the most to reduce tails/halos
formed in the early stage. LANSCE relies on the physics____________________________________________* This work was supported by Los Alamos National Laboratory’sLaboratory Directed Research and Development (LDRD) Program
under project 20230409MFR.
† en-chuan@lanl.gov
MOPB: Monday Poster Session
MC4.8 Superconducting RF

tune-up at the beginning of each run cycle, as we still yet
cannot reliably return to past stable operation points.
However, the physics tune-up procedures do not currently
address the halos/tails. For the DTL, an absorber/collector
pair [2] is used to measure the beam current above a given
energy threshold under a phase scan. The present
procedure only considers three measured parameters: theFull Width Half Maximum (FWHM), which represents thephase width of the acceleration bucket, the relative phasein the bucket, and peak-to-valley ratio (PVR) for the firstmodule to constrain the effects of the bunchers. For the
CCL, we use Beam Position and Phase Monitors (BPPMs)
for signature matching of a phase scan. This ensures thebeam, on average, is correctly accelerated [3]. However,this method does not easily demonstrate the picture of thelongitudinal capture. While many other facilities rely on
power measurements for each cavity to return to known
amplitude setpoints, LANSCE has also attempted such
effort [4]. However, LANSCE has yet to reliably
reproduce cavity amplitude setpoints based on power
measurements due to aging cavities and the problematic
performance of klystrons [5]. Therefore, beam-based
signature matching is the only reliable method for us todetermine the amplitude setpoints of each CCL module.
Therefore, an online multi-particle model for the physics
tune-up is critical for LANSCE to reduce the initial
optimization time by operators for every run cycle. In thisproceeding, we present an online software tool based on
the GPU-based HPSim [6-8] that quickly converts thephase scan results into intuitive pictures of the longitudinal
capture.

Figure 1: A schematic of LANSCE acceleration andbunching scheme. Both H+ and H- beam go through theirrespective Cockcroft–Walton (CW) generator and PreBuncher (PB), and merge into the same Main Buncher(MB). The beam delivered to WNR also goes through a
Low Frequency Buncher (LFB) before the PB. The Drift
Tube Linac (DTL) accelerates both H+ and H- to 100 MeV
while the Side-Coupled Cavity Linac (CCL) accelerates Hto 800 MeV.
MOPB084
223

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ONLINE MULTI-PARTICLE MODEL FOR LANSCE PHYSICS TUNE-UP
WITH HPSIM*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB085

E. Henestroza†, S. Sosa Guitron, S. Kurennoy, D.A. Dimitrov, J. Upadhyay
Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract
The Los Alamos Neutron Science Center (LANSCE) facility at LANL is considering an upgrade of its front end,
from the source to the end of a 100 MeV Drift Tube Linac(DTL). One of the main features of LANSCE is that it delivers several types of bunching systems to five users (Isotope Production Facility, Lujan Neutron Scattering Center,
Ultra Cold Neutron Center, Proton Radiography Facility“pRad” and the Weapons Neutron Research Facility“WNR”). The first three users accept bunch trains modulated at 201.25 MHz produced from quasi-DC beams. The
WNR facility requires the delivery of sub-nanosecond
bunches every 1.8 μs. At present the bunching system for
the WNR beam is prepared in a 750 keV Low Energy BeamTransport (LEBT) lattice. The proposed upgrade will needto manipulate short bunches for WNR at an energy of
100 keV to be injected into a 3 MeV RFQ. The quasi-DC
beams can be charge-compensated by the ionization of
background gas, which cannot be done for the shortbunches of WNR. A similar situation happens with thepRad beams. At such low beam energy, the uncompensatedspace charge of the bunch will require a special LEBT design that will work simultaneously for all types of beams
to be delivered by the LANSCE upgrade. We will describe
a new LEBT layout for the LANSCE Front End Upgradethat will be able to deliver the required beam bunches to all
facilities.

INTRODUCTION
The Los Alamos Neutron Science Center (LANSCE) accelerator delivers high intensity proton beams for fundamental science and national security applications since1972. LANSCE is capable of simultaneous H+ and H- beam
operations to multiple experiments requiring different time
structures. This is achieved upstream in the facility with a
combination of two 750 kV Cockcroft-Walton (CW) generators, a chopper and radiofrequency cavity pre bunchers,
and a Drift Tube Linac to accelerate the beam to 100 MeV.
The proposed LANSCE Modernization Project (LAMP) isevaluating critical machine upgrades necessary for continuous beam operations in decades to come. A significant
component of LAMP is replacing the two CW with a dualspecies 3-MeV Radiofrequency Quadrupole (RFQ). Thischange requires a full re-design of the LANSCE front-end
accelerator to deliver the existing and expanded capabilities of the facility.
A design of a concept for a Front End Upgrade of the
LANSCE Linac has been set up to perform a start-to-end___________________________________________* This work benefitted from the use of the LANSCE accelerator facility.
Work was performed under the auspices of the US Department of Energy by Triad National Security under contract 89233218CNA000001.
† henestroza@lanl.gov
MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transportmodeling of the system at the current development stage.
The components of the design are shown in Fig. 1. The sequence of the components is correct; however, the sketch
is not to scale.

Figure 1. Concept for a LANSCE Front End Upgrade.
The LANSCE Upgrade front-end concept discussed here
evolved from a design described in a previous report [1];the H- and H+ ion sources, the RFQ and the MEBT havenot changed. Here we will discuss the design of a multipurpose LEBT that will work simultaneously for all typesof beams to be delivered by the LANSCE upgrade.

CHARGE COMPENSATION IN THE LEBTThe LANSCE Front End Upgrade is required to deliver
625 μs beam macro pulses with specific time structures tothe present users. A chopper located in the H- LEBT provides such bunching systems.
The use of a 100 keV beam to inject into the 3 MeV RFQ
that replaces the Cockcroft-Walton generators turns the
LANSCE 750 keV LEBT into a 100 keV LEBT, thereby
increasing the space charge force substantially:(750/100)1.5 ~20. Therefore, there is a large difference inthe beam dynamics in the 100 keV LEBT among beampulses that can or cannot be charge compensated.
To study the beam dynamics in the LEBT, we can groupthe five types of beam structures in two groups.
The macropulses delivered to Lujan Neutron Scattering
Center, Ultra Cold Neutron Center and Isotope Production
Facility can be treated as long (625 μs) quasi-DC beams
where we expect to have in the 100 keV LEBT a large
charge-compensation by ionization of the background gas[2]. This type of macropulses will be referred as LBEGtype beams. The H+ beam delivered to the Isotope Production Facility is a DC beam, but the other two H- beams arebasically 625 μs pulses where 70 ns slices are removed
every 360 ns.
The Weapons Neutron Research Facility requires the delivery of sub-nanosecond bunches every 1.8 μs at the target. At present the bunching system for the WNR beam isprepared in a 750 keV LEBT where the macropulse ischopped every 1.8 μs to provide a 30 ns beam bunch to a
16.67 MHz Low Frequency Buncher that compresses thepulse to ~ 5ns to match the frequency (201.25 MHz) of the
750 keV-100 MeV DTL. Due to the sparsity of this time
MOPB085
227

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DESIGN OF A MULTI-PURPOSE LEBT FOR THE
LANSCE FRONT END UPGRADE*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB088

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

NEW CONCEPTS FOR A HIGH POWER 805 MHz RF AMPLIFIER FORLANSCE USING GALLIUM NITRIDE SEMICONDUCTORS*
J. T. M. Lyles†, J. D. Alvarez Prieto, S. A. Baily, M. S. Barrueta, J. T. Bradley III, E. N. Brown,
M. C. Brown, J. L. Castellano, B. N. Comiskey, T. W. Hall, S. I. Kwon, M. S. Prokop, S. Rocha,
M. B. Rodriguez, P. J. Van Rooy, S. J. Russell, J. A. Valladares, A. S. Waghmare
Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract
Los Alamos Neutron Science Center (LANSCE) uses a
coupled-cavity linac (CCL) to accelerate H- beam from100 to 800 MeV. This was the first CCL put into operation
anywhere in 1972 and is powered by forty-four 1.25 MW
805 MHz klystrons developed in the same era. A new initiative is underway to develop a replacement RF power amplifier that fits in place of one klystron with HV modulator
tank and is functionally equivalent or better in RF performance. Conventional LDMOS transistors based on silicon
have reduced power above 500 MHz and are also limited
in peak power by the maximum drain voltage (50-65 volts).
Changing wireless infrastructure is causing leading manufacturers to introduce and discontinue products within adecade. Long term operation of LANSCE requires continuity of product availability. We have chosen leading-edgehigh voltage Gallium Nitride (GaN) on Silicon Carbide
transistors to be able to reduce the number of active devices
and the complexity of power combing. GaN has inherent
higher temperature and voltage capability. We are testing
devices for 3.6 kW of saturated power at 100 volts, andimprovements are underway. Combining technology isalso under study as part of the overall system.

INTRODUCTIONLANSCE has operated as a 800 MeV proton and H- linac
since 1972. Presently protons of 100 MeV from the drift
tube linac are used for isotope production while a subsequent CCL accelerates H- beam from 100 to 800 MeV. This
normal conducting structure is powered by forty-four 1.25
MW 805 MHz klystrons, which all together provide approximately 44 MW of peak RF power and 5.3 MW of average power. These mod-anode klystrons are still available
using the same design as the original tubes. The LANSCE
linac is expected to continue operation until 2050, andthere are growing concerns about relying solely on thisvacuum electron tube technology for 25 more years. Meantime between failure for current klystrons is shorter than it
was for the original production tubes [1]. They rely on
86 kV beam voltage from conventional mains power___________________________________________* Work supported by the U.S. Department of Energy through the Los
Alamos National Laboratory, operated by Triad National Security, LLC,
for the National Nuclear Security Administration of U.S. Department ofEnergy (Contract No. 89233218CNA000001). Research presented inthis article was supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory under project
number 20240723DI.
† jtml@lanl.gov
MOPB088230

supplies and capacitor banks, which present their own setof technical difficulties that are beyond the scope of thispaper.
A new initiative is underway to develop a replacement
RF power amplifier that can fit in the space of one klystronwith a HV modulator tank. This will use a multitude ofSolid-State Amplifiers (SSA) combined to produce theequivalent or better performance than the klystron. Peakpower capability has been a hallmark for vacuum tubes,
where the thermal mass is large and the peak to average
power ratio is unity (CW) to as high as ten. For a SSA, thebest approach is operating in continuous mode, and this has
enabled SSAs to replace klystrons or inductive output
tubes at dozens of synchrotrons and storage rings worldwide [2]. Pulsed operation, such as for the LANSCE CCL,
requires considering the intrinsic peak capability of the individual junctions or channels inside transistors. Transistors require matching circuits adjacent to the input and output terminals, using discrete capacitors, inductors and microstrip lines. The functional block of transistor (single orpush-pull device) plus matching is a pallet. This is the basic
building block of all SSA.

TRANSISTOR CONSIDERATIONSSilicon transistors using laterally-diffused metal-oxide
semiconductor (LDMOS) construction are often rated at a
maximum operating DC (drain to source) voltage of 50-75
volts. LDMOS is a mature technology from multiple manufacturers and has powered wireless communication for
decades. They can be made from large wafers in conventional silicon foundries so the price per watt is attractive.
These devices can generate up to 2 kW of saturated peak
power below 500 MHz but at 805 MHz the gain and peak
power drops. The drain to source capacitance of these devices, related to their construction, limits further improvement in their frequency-power product. As upcoming wireless technology such as 6G requires considerably more
bandwidth into GHz bands, LDMOS is less viable, andnew transistor technologies have come into use.
Gallium Nitride (GaN) on Silicon Carbide (SiC) is a highelectron mobility transistor that is becoming available frommultiple sources [3]. The wide bandgap of the semiconductor allows for higher breakdown voltage rating while operating at increased channel temperature. GaN RF transistors
operating above 100 volts DC are now available [4, 5] at
UHF and L band. Matching of the drain terminal to fifty
Ohm transmission line is easier as the transistor load impedance is proportional to the RF drain voltage. When
comparing transistors it is important to understand the class
MOPB: Monday Poster Session
MC4.6 RF power sources and power couplers

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB090

M. Rautela† ,1 , A. Williams1 , A. Scheinker1
1
Applied Electrodynamics (AOT-AE), Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract
The problem of estimating upstream six-dimensional
phase space given downstream measurements of charged
particles is an inverse problem of growing importance. In
this work, we propose a latent evolution model (LEM) to
invert the forward spatiotemporal beam dynamics. In thistwo-step self-supervised deep learning framework, we firstuse a conditional variational autoencoder (CVAE) to transform 6D phase space projections of a charged particle beam
into a lower-dimensional latent distribution. We then autoregressively learn the inverse temporal dynamics in the latent
space using a long-short-term memory (LSTM) network.
The coupled VAE-LSTM framework can predict 6D phasespace projections in upstream accelerating sections given
single or multiple downstream phase space projections as
inputs.

INTRODUCTION
Particle accelerators are complex, time-varying, highdimensional systems governed by hundreds to thousandsof radio-frequency (RF) cavity and magnet parameters.
The dynamics of charged particle beams in accelerators
emerges as spatiotemporal phenomena, characterized by
the temporal evolution of a six-dimensional phase space(𝑥, 𝑦, 𝑧, 𝑝𝑥 , 𝑝𝑦 , 𝑝𝑧 ). The solution of such dynamical systems
can be computationally demanding due to the intricate interplay between temporal evolution and detailed spatial features.
Machine learning and deep learning methods have shown
significant promise for challenging different spatiotemporal dynamical problems. Recently, latent evolution models(LEM) have gained traction for solving various dynamicalsystems [1–5]. The key idea is to decompose the learning
problem into spatial and temporal learning, which are later
coupled to make predictions.
Recent applications of Latent Evolution Models (LEM)
for addressing beam dynamics in particle accelerators haveshown significant progress. In Refs. [6–8], an adaptive virtual 6D phase space diagnostic was developed, where an
autoencoder compresses high-dimensional 6D phase space
projections into a low-dimensional latent space. Adaptive
feedback within this latent space is then used to track theproperties of an unknown, time-varying beam as accelerator
parameters evolve. In Refs. [9, 10], a conditional variational
autoencoder combined with an autoregressive LSTM is employed to generate and predict beam dynamics throughout
the accelerator based on initial module measurements.
∗ Work supported by the LANL LDRD Program Directed Research (DR)project 20220074DR† mrautela@lanl.gov

MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

The solution of inverse problem to estimate upstream
phase space is essential for characterizing the beam in earlier
sections of the accelerator, which in turn helps to understandbeam dynamics, minimize beam losses, and optimize accelerator performance. However, limited studies are conductedon predicting the upstream phase space of charged particles
based on downstream measurements. In Ref. [8], an adaptive
ML approach has been proposed to map output beam measurements to input beam distributions. In Ref. [11], neuralnetworks are integrated with differentiable particle tracking
to learn mappings from measurements to initial phase space
distributions.
In this paper, we propose a latent evolution model (LEM)
that predicts the upstream 6D phase space from downstream
measurements. The model uses a conditional VAE to learn
the low-dimensional latent distribution of 15 unique phasespace projections, followed by an autoregressive LSTM toreverse the forward temporal dynamics in the latent space.
This coupled network enables the prediction of upstream
phase space projections based on single or multiple downstream measurements.

METHODS
Charged Particle Beam Dynamics
The behavior of charged particles in accelerators is influenced by numerous parameters, such as radio frequency cavity fields and magnetic field strengths. These parameters aremanually adjusted to minimize beam loss, but this process istime-consuming, often leading to suboptimal performance.
Additionally, limited non-destructive beam measurements
and short run times complicate data collection. It is crucial
to understand beam dynamics for optimal accelerator performance. More details about the optimization and tuning
challenges of the LANSCE accelerator are given in Ref. [12].
The dynamics of a beam’s phase space density function
are governed by the relativistic Vlasov equation𝜕𝜌𝜕p= −v ⋅ ∇x 𝜌 +⋅ ∇p 𝜌,
(1)
𝜕𝑡
𝜕𝑡
𝜕p
= 𝑞 (E(𝑥, 𝑦, 𝑧, 𝑡) + v × B(𝑥, 𝑦, 𝑧, 𝑡)) ,(2)𝜕𝑡with v and p representing velocity and relativistic momentum:𝑑𝑥 𝑑𝑦 𝑑𝑧v = ( , , ) , p = (𝑝𝑥 , 𝑝𝑦 , 𝑝𝑧 ) = 𝛾𝑚v,
𝑑𝑡 𝑑𝑡 𝑑𝑡
1𝛾 =, 𝑣 = |v|,
(3)
√1 − 𝑣2 /𝑐2
where 𝑐 is the speed of light [13]. The electromagnetic
fields, E and B each have external and beam-based sources.
MOPB090
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LATENT EVOLUTION MODEL FOR TIME-INVERSION OF
SPATIOTEMPORAL BEAM DYNAMICS∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB091

M. Sanchez Barrueta†, H. Xu, Los Alamos National Laboratory, Los Alamos, USA
Abstract
Space-borne accelerator technologies suffer from significant electron beam loss during beam acceleration and excessive energy spread of the output beam. Los Alamos National Laboratory is proposing a deployable and compact
solution using electrostatic potential depression (EPD) toachieve higher bunching, lower beam loss, and smaller energy spread, with an electron bunch repetition rate of
5.7 GHz. This buncher system involves two EPD sections,each electrically insulated from the RF cavities and with aseparate high voltage power supply, whose leads will haveto reach through vacuum and the insulator to bias the specific section of the buncher. This presents considerable
challenges due to the triple junction problem and the presence of parasitic radiofrequency leaking through the electrostatic high voltage gaps.

INTRODUCTION
In compact radiofrequency (RF) accelerator applications, the electron beam source is usually a direct-current(DC) electron gun. If the DC electron beam is sent directly
into the RF accelerator, only a very small portion of thebeam will fall within the desired longitudinal acceptanceof the RF accelerator. In order to maximize the DC electron
beam capture in the RF accelerator, in large-scale, facility
accelerators, meter-long buncher sections are used in thebeamline. Those buncher structures consume external RF
power at a megawatt (MW) level. For compact accelerators, the high-power buncher scheme is inefficient, andthus unadoptable.
Recently, at Los Alamos National Laboratory (LANL), a
novel type of electron beam buncher is under development[1]. The buncher is intended for application on a spaceborne electron RF accelerator, and it is intended for the purpose of increasing the usable portion of the DC beam generated, meanwhile keeping the energy spread of the electron bunch at a low level. Such an electron beam buncher
will significantly benefit space missions where an RF accelerator is entailed, such as the Beam-Plasma Interactions
Experiment (Beam PIE) [2].
The electron beam buncher was designed based on acompact, high-efficiency klystron architecture [3], theunique feature of which is the utilization of electrostatic
potential depression (EPD) inserts. In the klystron architecture, an EPD insert, or section, refers to a short sectionof the metallic beam pipe that is applied with a negative
high voltage (HV). The HV-biased beam pipe is insulated
from other parts of the klystron, which are grounded. The___________________________________________* Work supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory under project number
20240136ER.
† msb@lanl.gov
MOPB: Monday Poster Session
MC2.2 Electron linac projects

EPD sections cause the electron beam bunching formation
to take place over a very short distance, allowing the entire
klystron circuit to be compact. In this proceeding, we report the basic architecture of the electron beam buncher
and introduce the design considerations of the HV feed aswell as the insulators. We also discuss the parasitic mode
excitation by the pre-bunched electron beam transiting
across the HV gaps of the EPD sections. Our electromagnetic and particle-in-cell (PIC) simulations were performed
using the CST Simulation Suite [4].

BUNCHER CONCEPTUAL DESIGN
The buncher architecture takes after a two-cavity klystron circuit, assisted by the EPD sections for achieving
compactness, as presented in Fig. 1. An electron gun generates pulsed DC electron beam, and the solenoid focuses
the electron beam into the buncher circuit. Inside thebuncher, the beam focusing is provided by permanent magnets, which were designed to be tunable [1], as inspired byan ongoing project at SLAC [5]. The input cavity provides
the initial energy modulation by the longitudinal RF electric field, at a frequency of 5.7 GHz. When the modulated,or pre-bunched, electron beam enters the first EPD section(EPD-1), its average kinetic energy is significantly reduced. However, the energy difference among the electrons
is preserved. As a result, the wave-break in the longitudinal
phase space occurs over a very short distance. When theelectron beam leaves EPD-1, its original kinetic energy isrecovered. The idler cavity in the downstream then further
adjusts the longitudinal phase space of the electron beam
to allow subsequent enhancement of the bunching formation. The function of EPD-2 is identical to EPD-1, maximizing the bunching level over a short distance. The
bunched electron beam then enters the 5.7-GHz RF accelerator in the downstream.

Figure 1: Electron buncher two-cavity conceptual design
illustration. Permanent magnets between each two polepieces are suppressed. Point A and B are placed at the center of the re-acceleration gaps of the EPD-1 and EPD-2 sections, respectively. The blue-colored rectangles are intended for parasitic mode discussion in a later section.
MOPB091
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HIGH-VOLTAGE FEED DESIGN FOR ELECTROSTATIC POTENTIAL
DEPRESSION IN AN RF ACCELERATOR*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB092

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

LINAC MODULE PHASE SCAN IN HPSim∗
M. J. Kay† , P. M. Anisimov, A. J. Braido, E.-C. Huang, J. K. K. Quemuel, L. J. Rybarcyk
Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract
The side-coupled cavity linac (CCL) at the Los Alamos
Neutron Science Center (LANSCE) is tuned by matchinga single-particle model to the RF phase signature of themodules. In the future, the High-Performance Simulator(HPSim), a GPU-powered, 6-D particle tracking code, will
be used to reveal additional information that will assist withtuning. In this proceeding, the status of the HPSim-based
Phase Scan Signature Matching (PSSM) routine is presented,
along with the outlook for its future implementation.

INTRODUCTION
The LANSCE accelerator at Los Alamos National Laboratory (LANL) supplies beam to five user facilities andsimultaneously accelerates H+ and H− [1]. The CCL is
made up of 44 accelerating modules, which accelerate theH− beam from 100 MeV to 800 MeV (Fig. 1). The 805-MHz
RF field that powers each module is supplied by a different
klystron, causing the amplitude and phase of the RF inside
one module to be independent of all others. As a result, each
module must be tuned individually before the start of the runcycle. PSSM is used to tune the CCL modules, in which thephase of the H− beam after a module is measured while theRF phase is scanned over a full cycle [2]. A fitting algorithm
then attempts to match the output of a single-particle modelto the measured phase scan signature to extract parameters
necessary to tune the module.
The High-Performance Simulator (HPSim) code will compliment the single-particle model used in PSSM by revealing
additional information about the tune. HPSim is a 6-D particle tracking code that is powered by GPUs [3]. The code
was developed at LANL and contains a detailed model of the
LANSCE linac. The signature feature of HPSim is its speed,which allows it to be used as an online simulation tool toassist with beam recovery during startup [4, 5]. HPSim cangive information about the bunching and RF capture qualitythat the single-particle model cannot. In this proceeding,
it is shown that HPSim reproduces an archived phase scansignature measurement as accurately as the single-particle
model, while also retaining the full 6-D beam distribution.

CCL MODULE TUNE-UP
Tuning a CCL module amounts to ensuring the RF field
amplitude and output beam energy are at the design values
and that the beam exits the module properly bunched. The
two “knobs” available for tuning are the RF amplitude setpoint (ASP) and phase setpoint (PSP). Although neither is∗ This work was supported by Los Alamos National Laboratory’s Labora-

tory Directed Research and Development (LDRD) program under project
number 20230409MFR.
† mkay@lanl.gov
MOPB092240

750-keV H
CockcroftWalton
Injectors H-+

201.25-MHz,
100-MeV
Isotope Production Facility
Proton Radiography
Drift Tube
Linac
805-MHz, 800-MeV Side Coupled-Cavity Linac

Ultra-Cold Neutrons
Area A (inactive)

Module 1-4

Module 5-48

ProtonStorage Ring
Weapons Neutron
Research Facility

Lujan Center

Figure 1: The LANSCE accelerator and user facilities.
calibrated to match the actual value, there is a one-to-one
relationship. Tuning a CCL module is an iterative processes
that uses PSSM to determine the correct ASP and PSP.

Phase Scan Measurement
PSSM requires the beam phase to be measured at a point
after the module. A beam position and phase monitor(BPPM) measures the phase of the beam relative to a 201.25MHz reference signal (Fig. 2). First, the RF is turned off,
and the BPPM measures the phase of the beam after it drifts
through the module. Then, the RF is turned on, and the
BPPM measures the phase of the accelerated beam while
the PSP for the RF is scanned between ±180°. The difference between the phases measured with the RF on and off
is plotted over the range of PSPs to produce the phase scansignature curve.

Phase Scan Signature Matching
A fitting algorithm then attempts to reproduce the phasescan signature with a single-particle model. An example
of a fit for CCL module 5 is shown in Fig. 3. The fit isused to extract three parameters: the fractional amplitudeof the RF field, the input beam energy offset, and the input
beam phase offset. The best-fit values of those parameters
are used to calculate the output energy of the beam at each

Dmodule

DBPPM

Accelerating ModuleH‒ beam
RF Phase

Reference RF LineBPPM
Figure 2: Phase scan measurement setup.
MOPB: Monday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB093

M. Pieck†, C. D Hatch, H. A. Watkins, E. E. Westbrook
Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract
From being the first computer-controlled accelerator,
through its 52-year long operational history, today the
LANSCE Instrumentation and Control (I&C) systemshows little resemblance to its early days. However, its
maintainability depends on the ability to restore, or repair
failed systems. Complicating this task is the undeniable
fact that technology has significantly evolved over the last
decades and that older components and systems, while still
performing their function, have become obsolete and unmaintainable. When a technology migration path isn't viable to ensure I&C system maintainability, the only alternative is to upgrade to a new technology. Consideration needs
to be given so that the new technology platform seamlessly
integrates with the existing I&C infrastructure while allowing for technological progress. We discuss from the
LANSCE’s I&C engineering perspective the universal
challenges older facilities are facing. We also provide a
I&C system architecture overview.

LANSCE USER FACILITY
The Los Alamos Neutron Science Center (LANSCE) has
been in operations for over 52 years. The multifunctional
facility has grown over the years and now has five distinct
state-of-the-art experimental facilities which provide thescientific community with intense sources of protons andneutrons, with the capability of performing experiments
supporting civilian and national security research [1].
Without a properly functional LANSCE accelerator noneof these experimental facilities could fulfill their mission.
Hence, it is critical to plan for and appropriately fund theupkeep of the necessary LANSCE accelerator systems.

INTRODUCTION
Technological advancements have revolutionized control systems, making them smarter, more efficient andtransformative. Control systems have surpassed previous
limits offering intelligent features. This progress has ushered in an era of automation and machine learning, shaping
a world of new possibilities.
An Accelerator Instrumentation and Controls (I&C)
system realtity check, is that many of the accelerator facilities around the world are lasting longer, extending their
end-of-life. At the 2024 Accelerator Reliability Workshop,__________________________________________________________* This work was supported by the U.S. Department of Energy through theLos Alamos National Laboratory. Los Alamos National Laboratory is operated by Triad National Security, LLC, for the National Nuclear Security
Administration of U.S. Department of Energy (Contract No.
89233218CNA000001).
† pieck@lanl.gov, LA-UR-24-28976

MOPB: Monday Poster Session
MC4.5 Other technology

an informal survey revealed that numerous facilities are
more than 40, and 50 years old with a few of them evenolder than 60 years.
During the lifetime of a facility, some of the I&C systems have been very likely modernized. Moreover, as anaccelerator increases in size and complexity so do its I&C
systems. As a result, I&C systems have often accumulated
a wide variety of hardware form factors and software methodologies that challenge maintainability and longevity.
I&C engineers are faced with the daunting task of maintaining and modernizing their systems, often under thetight budgetary and schedule constraints of an operating
accelerator facility with an enduring mission.

ACCELERATOR I&C SYSTEM LIFESPAN
External observers may perceive an accelerator I&C system as operating “just fine”, while others, usually those
who are “arms deep” into things, can have a totally different opinion. System complexity, component diversity andinterdependencies, deferred maintenance, and technology
obsolescence all have significant and compounding effects
on overall I&C system maintainability and lifespan.
Accelerator I&C lifespan information is not widely published, and the information that is published does not provide a complete picture. This is probably, at least in part,
because large accelerator I&C systems don’t get upgradedin their entirety all at once.
Driven by budgetary and operating schedule constraints,
I&C engineers often focus on partial upgrades to keep up
with technology maturation of individual systems. Consequently, accelerator I&C systems continuously undergo
some form of modernization effort. Hence it is difficult toreport on their exact lifespan. Nevertheless, it is importantto understand the lifespan expectancy of systems since it
directly impacts future work scope, related labor, material
needs, and consequently required funding.
Given that accelerator I&C systems rely for the most parton industry standards, one can often find life expectancy
information for single vendor-based systems. It becomes
more challenging when systems are composed of multiple
components from different vendors. This may be complicated by software and hardware interdependencies.
Lifespan information about general category is available: Switches: 5–7 years. Routers: 3–4 years. Firewalls: 5–
8 years, instrumentation 10-15 years, PLCs/Industrial automation controller 10-20 years, desktop computer 5-7
years, FPGAs 3-5, windows operating system ~10 years,
Linux operating system 10 years. I&C engineers need tounderstand, document, and track the specific lifespan for
their equipment to address the risk to support operations in
a pre-emptive manner.
MOPB093
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LANSCE ACCELERATOR INSTRUMENTATIONAND CONTROL TECHNOLOGY CHOICES*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB095

S. J. Russell†, J. Bradley, E. Brown, B. Carlsten, G. Dale, M. Gulley, J. Lyles, J. Tapia
Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract
The Los Alamos Neutron Science Center (LANSCE) accelerator is a MW-class H-/H+ 800 MeV linear accelerator
that serves five distinct user facilities that support Los Alamos National Laboratory (LANL) national security missions, commercial applications, and the Department of Energy Isotope Program (DOE IP). Now into its sixth decadeof continuous operation, major accelerator systems areshowing their age with decreased reliability and diminished vendor support due to equipment obsolescence. Withplans to continue LANSCE operations for several more
decades, LANL is exploring different avenues to modernize large portions of the accelerator. We will present thecurrent status of those plans and an overview of supporting
R&D.

proliferation, and criticality safety. Serves as a user facility for electronics testing for industry and global security agencies.

THE LOS ALAMOS NEUTRONSCIENCE CENTER
In 1972 the Los Alamos Meson Physics Facility(LAMPF) began operations for a 20-year basic nuclear
physics program. The most powerful proton beam in theworld, until the early 2000s, LAMPF pioneered technologies such as the side coupled cavity linear accelerator anddual species acceleration. When its original mission ended,
LAMPF was re-branded as the Los Alamos Neutron Science Center (LANSCE) and repurposed as a user facility
for nuclear weapon stockpile stewardship, basic science,industry, and isotope production [1]. Highlighting the versatility of the machine, LANSCE currently supports five
distinct user end stations (Fig. 1):
 Isotope Production Facility (IPF) – IPF produces medical and other isotopes for the DOE IP, short-lived isotopes for defense programs, counter and non-proliferation, and criticality safety studies
 Proton Radiography (pRad) [2] – pRad employs 800
MeV protons to do dynamic imaging of shock and detonation events.
 Ultra-Cold Neutron Facility (UCN) [3] – Uniqueprobe for basic nuclear physics science.
 Lujan Neutron Scattering Center (Lujan Center) [4, 5]– Provides spallation neutrons for neutron scatteringand imaging and provides neutrons for materials science.
 Weapons Neutron Research Facility (WNR) [5] – Enables nuclear physics for defense programs, counter____________________________________________* Work was performed for U.S. Department of Energy by Triad National
Security, LLC, contract 89233218CNA000001 and through the Laboratory Directed Research and Development program of Los Alamos National Laboratory, under project number 20240723DI† srussell@lanl.gov

MOPB: Monday Poster Session
MC3.4 Proton linac projects

Figure 1: LANSCE [1].

LANSCE PRESENT STATUS AND
FUTURE PLANSLANSCE Present Status
In 2008 LANL embarked on an eight-year program to
upgrade targeted LANSCE systems to both restored historical operating capability and to sustain future operation [6].
This involved an upgrade of the 201.25 MHz radiofrequency (RF) system that drives the LANSCE drift tube linear (DTL) accelerator, which accelerates the beam to
100 MeV, and procurement of 45 new 805 MHz klystrons
from Communications and Power Industries to serve as
spares for the 805 MHz High Power RF (HPRF) system,
which powers the LANSCE coupled cavity linear (CCL)
accelerator and boosts the beam energy from 100 MeV to800 MeV. These new tubes are nominally identical to theoriginal 1960s era design and were delivered by the end of
2014. The 201.25 MHz system upgrade was completed in2016 [7].
Although this modest sustainment effort did in factachieve its purpose, ensuring operation of LANSCE until
2020, it was not a long-term solution. LANL and the National Nuclear Security Agency (NNSA) have since realized that operation of LANSCE is needed until at least
2050. However, at 52 years of age modernization of the facility is now essential as reliability is now a major concern(Fig. 2). In 2019, for example, a crack developed in one of
the four DTL tanks due to decades of thermal cycling. Fortunately, the location of the damage was accessible and was
MOPB095
247

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UPDATE ON THE STATUS OF THE LOS ALAMOS NEUTRON SCIENCECENTER ACCELERATOR MODERNIZATION*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB097

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

AUTOMATION OF SAMPLE ALIGNMENT FOR
NEUTRON SCATTERING EXPERIMENTS
B. Pritchard, M. Henderson, J. P. Edelen, RadiaSoft LLC, Boulder, CO, USA
Abstract
Sample alignment in neutron scattering experiments is
critical to ensuring high quality data for the users. This
process typically involves a skilled operator or beamline
scientist. Machine learning has been demonstrated as an effective tool for a wide range of automation tasks. RadiaSoft
in particular has been developing maching learning tools
for a range of accelerator applications including beamline
automation. In this poster we will present recent developments for selecting and aligning multiple samples at the
HB-2A powder diffractometer at the High Flux Isotope Reactor (HFIR).

INTRODUCTION
Neutron beam diffraction experiments are a critical toolfor determining the atomic structure and physical characteristics of materials. The HB-2A diffractometer at Oakridge
National Laboratory (ORNL) provides data primarily forthe purpose of determining the magnetic structure of powder samples [1]. HB-2A has an open instrument layout andmultiple rotational and translational degrees of freedom thatallow for rapid cycling between up to three samples placedon the sample stage at a time (see Fig. 1), where a concentrated neutron beam of constant wavelength supplied by theHigh-Flux Isotope Reactor (HFIR) interacts with the samples. Neutron detectors partially encircling HB-2A are used
to capture the resulting neutron diffraction data, and a diagnostic neutron camera at the end of the beamline provides a2D view of the sample orientation and location within thebeam.
Currently, HB-2A relies on a skilled operator to manually identify approximate sample centroids in the diagnostic
camera images and align the samples with the neutron beam.
Operators uses a graphical user interface (GUI) to initiate
motor controls, a procedure which must be repeated continuously over an experiment to achieve the manual adjustments
needed to keep the sample correctly placed within the beam.
Although this process is relatively straightforward and sufficient for achieving the scientific goals of an experiment,
it requires the expenditure of labor hours by highly skilled
beamline scientists whose time could be better spent onhigher-level operations and experiment planning. The alignment process at HB-2A and other beamlines is therefore aprime target for automation.

SAMPLE SEGMENTATION PROBLEM
In previous work, images from the diagnostic neutron
camera at HB-2A have been used to orient the sample within
the beam using both the standard manual procedures as wellas an automated alignment procedure recently developed by
MOPB097250

Figure 1: HB-2A sample stage.
RadiaSoft. The automated procedure makes use of a UNet, a
type of convolutional neural network (CNN) used in machine
vision [2], to produce binary masks of sample images which
are then used to identify sample centers and align themwithin the neutron beam. However, the automated alignment
processes currently deployed at HB-2A rely on the condition
that the masks produced by a UNet contain only a single
contiguous sample. The use of a multi-sample environment
to enhance experimental efficiency at the beamline therefore
poses a challenge for automated alignment, as secondary andtertiary samples cannot easily be excluded from diagnostic
camera images under most circumstances.
In order to address the automation challenge posed by
the multi-sample environment at HB-2A, we have begun toaugment the alignment procedure to include an additional
instance segmentation task. In this task, masks that contain binary information indicating whether or not each pixel
contains a sample are processed to add an additional labelthat indicates which (if any) sample is present in the pixel.
We utilized a basic form of connected component analysis(CCA) to achieve this processing by computing average 1D
image and sample mask profiles, segmenting pixels belonging to distinct clusters, and assigning group labels basedon the segmentation. This process is described in more detail below, and is now being integrated into the alignment
software deployed at HB-2A.

METHODS
Static Imagery
Static images from the diagnostic neutron camera as wellhas masks available from previous work were used in development and testing. All software developed for this purpose
was written in Python and tested using a command line
interface and the rscontrols framework developed by RadiaSoft [3]. To ensure the best outcome possible and provide agreater level of robustness to the segmentation efforts, twoseparate segmentation approaches were tested. The first approach attempted to produce sample segmentation using justthe raw neutron camera image data (Fig. 2, left) which is
MOPB: Monday Poster Session
MC4.5 Other technology

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB098

J. P. Edelen∗ , J. Einstein-Curtis, RadiaSoft LLC, Boulder, CO, USA
A. Diego, M. Kravchenko, R. Berry, RadiaBeam, Santa Monica, CA, USA
J. Krasna, COSYLAB, Ljubljana, Slovenia
Abstract

Table 1: Parameters for the LLRF System

RadiaSoft and RadiaBeam are partnering on the development of a low level RF control system to support a 100 MeV
C-Band LINAC. Our system utilizes a Keysight data acquisition system and arbitrary waveform generator to drive the
LINAC. The controllers are fully integrated with EPICS
and are actively being commissioned. In this presentation
we will provide an overview of the design architecture, discuss details of the epics integration, and show initial results
controlling a photoinjector.

INTRODUCTION
The Low-Level Radio Frequency (LLRF) control system
is primarily responsible for delivering RF to amplifiers, receiving and processing signals for the various RF diagnostics,
and control of the RF cavities to include phase, amplitude,
and frequency. When building a LLRF system there are anumber of design considerations that lead to the choice of
frequency parameters, digital vs analog, and how to modulate the RF signals. One of the most common architecturesutilizes an intermediate frequency that is used for digitization and an analog system to perform up and down conversion [1]. However, base-band modulation has also been used,
for example the Swiss FEL utilized such an architecture [2].
Additionally, modern electronics are making systems that
perform direct digital down-conversion more popular [3].
For C-Band there are limited commercial options for direct
digital sampling that are also cost effective for a modest
scale system. This is largely due to the development timerequired and operating in unusual modes such as the first
Nyquist band. Moreover, the technical challenges associatedwith base-band modulation and noise mitigation makes adigital system operating at an intermediate frequency more
attractive. As such we chose to build a COTS system basedon digitization at a reasonable intermediate frequency withcost effective solutions. Figure1 shows a functional block
diagram of our COTS LLRF system. Here we highlight thenotable interconnections and signals. For this system, we
have a common local oscillator that is distributed to all of
the analog electronics. The digital system generates a clean
reference signal that is re-distributed to the LLRF system asa phase reference and also distributed to the timing systemand the laser system for phase locking. The parameters for
the LLRF system are given in Table 1.
This paper provides an overview of the digital and analog
components of the LLRF system as well as measurementof losses through the downconverter and amplitude stability
measurements. We also describe the EPICS integration at∗ jedelen@radiasoft.net

MOPB: Monday Poster Session
MC4.4 Low level RF

Parameter

Value

RF
IF
LO
Laser
Sample Rate
ADC
DAC

5712 MHz
100 MHz5812 MHz476 MHz
500 MS/s
14 bit16 bita high level and provide a brief overview of the high levelapplications used to control the accelerator.

DIGITAL SYSTEM DESIGN
The digital system is comprised of a an M3102A PXIeDigitizer from Keysight and an M3201A PXIe Arbitrary
Waveform Generator also from Keysight. Our AWG resolution is 16 bit at a 500 MS/s sample rate. The digitizer
resolution is 14 bit at a 500 MS/s sample rate.
The choice of intermediate frequency is largely determined by the available digital components and the constraints on RF filtering, This typically is in the 10 – 100
MHz range. Our initial choice of the intermediate frequency
is 100 MHz. This is to allow for good isolation between IF
signals, RF signals, and baseband signals. When convertingfrom RF to IF, the RF signal at 5712 MHz is mixed with the
LO at 5810 MHz. This will generate a 100 MHz signal anda 11524 MHz signal. The 11.5 GHz signal will be filteredout using analog components leaving the 100 MHz signal.
The IF signals will be digitized at a rate of 500 MS/s whichis readily available with modern digitizers. The choice of adigital system that is 2.5x Nyquist will provide higher signal
quality while maintaining a reasonable cost. The digitizers
have a bandwidth of up to 200 MHz and we will show resultsof our system with an IF of up to 175 MHz. To extract the
RF waveforms the 100 MHz signal is mixed digitally withanother 100 MHz signal giving a baseband waveform and a
200 MHz signal. In order to resolve the cavity dynamics, weneed a minimum of 20 MHz bandwidth at baseband. Having
200 MHz of space between the baseband signal and the secondary signal generated by the IF downmixing relaxes theconstraints on the filter design and reduces the need for highorder filters that cause ringing and other unwanted effects.
The arbitrary waveform generator has built in I/Q modulation for phase coherent signal generation. It can generate
sinusoidal signals with envelope and phase modulation all
synchronized to an internal reference clock. The DACs are
16 bit which provides a high level of precision for the RF
MOPB098
253

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LOW-LEVEL RF SYSTEM DEVELOPMENT FOR A C-BAND LINAC

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB099

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

COMMISSIONING AND PERFORMANCE OF A C-BAND LLRF SYSTEMAT RADIABEAM
J. P. Edelen∗ , J. Einstein Curtis, RadiaSoft LLC, Boulder, USA
A. Diego, M. Kravchenko, R. Berry M., RadiaBeam, Santa Monica, USA
J. Krasna, COSYLAB, Ljubljana, Slovenia
Abstract
RadiaBeam and RadiaSoft have been developing a LLRF
system for a 100 MeV C-band LINAC. The system is basedon a Keysight PXIE arbitrary waveform generator and ADCs.
We are in the process of commissioning our system and validating its performance. In this presentation, we will provide
details on amplitude and phase calibration, improvements
to signal conditioning, comparisons between measurements
and simulations, and performance of our pulse to pulse feedback scheme.

INTRODUCTION
RadiaSoft is leading the development of a LLRF system insupport of a C-band test accelerator being constructed at RadiaBeam. This machine contains staged acceleration which
requires phase synchronization between cavities and therefore a complete LLRF system. The system is comprised ofa digital arbitrary waveform generator that produces a modulated 100 MHz signal, an analog upconverter that mixes
the 100 MHz signal up to 5712 MHz, an analog downconverter that mixes measured signals down to 100 Mhz, and adigitizer that records the 100 MHz signals for processing by
our LLRF software. Our system also comprises timing andreference signal generation. The parameters for the LLRF
system are provided in Table 1.
Table 1: Parameters for the LLRF System
Parameter

Value

RF
IF
LO
Laser
Sample Rate
ADC
DAC

5712 MHz
100 MHz5812 MHz476 MHz
500 MS/s
14 bit16 bitThis paper is focused on improvements to the signal processing performed in software, calibration of our measurements, and initial performance of our pulse-to-pulse feeback
algorithms.

SIGNAL CONDITIONING
Our system performs signal processing in software after recording raw 100 MHz pulses. After the ADC records
the signal, it is passed through our EPICS IOC to a Python∗ jedelen@radiasoft.net

MOPB099
256

Figure 1: Amplitude (red) and phase envelope (blue) forthe hilbert method of envelope detection and the improved
envelope reconstruction using a traditional downconversion
implemented in Python (black dashed).
modules. Specifically, we utilize the scipy.signal function
hilbert [1], to reconstruct the amplitude and phase of the
100 MHz signals. The function uses Fourier transforms tobuild a complex representation of the input time domain
signal. While an efficient envelope detection method, we
have noticed the resulting waveforms have residual noise,
Fig. 1. A frequency analysis of these waveforms, Fig. 2,
shows the spectra of the hilbert reconstruction of the amplitude signal with a 100 MHz component and a 200 MHz
component. To correct for this we implemented a traditional
downconversion in the Python signal processing module.
Here we mix the incoming 100 MHz signal with a 100 MHz
reference followed by a low pass filter to remove the higher
harmonics. The resulting signals and frequency spectra areshown in the dashed lines in both Figs. 1 and 2 respectively.
Here we can see that the improved method for extracting thesignal envelopes no longer have the 100 MHz and 200 MHz
leakage and the envelopes signals are significantly smoother.

SIGNAL CALIBRATIONS
During commissioning we calibrated the signals measured
in the ADCs to be in units of megawatts. The ADC has arange of plus-minus four volts. The losses in the systemwere measured using a network analyzer and are provided inTable 2. Here we are considering two channels measuring
forward power for the two LINAC sections. The directional
couplers are identical to three significant figures along withthe attenuators. The cables had some slight variation and
MOPB: Monday Poster Session
MC4.4 Low level RF32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB101

M. Henderson, D. Abell, D. Bruhwiler, J. P. Edelen, J. Einstein-Curtis
RadiaSoft LLC, Boulder, CO, USA
A. Diego, R. Agustsson, RadiaBeam, Santa Monica, CA, USA
Abstract
Simulation tools are critical to the prototype and validation of control algorithms prior-to and during commissioningof LLRF systems. Moreover, for industrial systems, diagnostics that are available on test systems and in laboratory
accelerators are not always available in the field. RadiaSoft
has been developing an RF simulator suite that allows for
rapid prototyping of control algorithms in a fully integrated
epics environment. As part of this process, we have performed extensive testing and bench-marking using a novel
C-band test cavity with a range of diagnostics. This poster
provides an overview of the simulator, the physical models
which make it up, and results for an example system withtwo cavities and other typical hardware elements.

INTRODUCTION
Most particle accelerator facilities feature some numberof RF cavities and associated low-level (LLRF) control systems, whether as primary mechanisms for acceleration or for
use in other subsystems (e.g., injection modules). However,utilizing these devices for secondary purposes such as controls development can be costly in both time and resources,
and can impede normal experimental operations.
To that end, RadiaSoft has designed, tested, and deployeda robust RF simulator for developing LLRF control algorithms, input-output control (IOC) software, and user interfaces (UI). The simulator is integrated with the EPICS
framework for experimental controls, and can be run througha number of modalities, including basic command line interfaces, Python scripts or Jupyter notebooks, and direct EPICS
connections. It describes RF signal propagation using a standard scattering matrix approach and cavity dynamics using
an effective circuit model derived in previous work for application to superconducting cavities.
Using our simulator, we have successfully tested several
practical LLRF feedback control methods (including PID
loops and filters), modeled systems of interest for research
applications, and even studied the use of machine learning
as a means for noise reduction in industrial RF systems. The
simulator itself has been key to the success of these and otherongoing efforts, and will described in greater detail below.

RF SYSTEM MODELING
Cavity Model
Development of our RF simulator began with a simple
effective RLC circuit model which accounts for a number ofsystem characteristics, including: coupling and quality factors, frequency, drive amplitude and phase, pulse duration,and cavity detuning. The associated model dynamics are
MOPB: Monday Poster Session
MC4.4 Low level RFbased on equations previously derived in [1] and [2], andan additive white Gaussian noise (AWGN) model for simulated measurements. Simulation is carried out by solving a
differential equation for the voltage transmitted by a cavity,
which is a function of both the current transmitted voltage
and effective applied current supplied to the cavity:𝑑V𝑡−𝜔= [ 1/2
Δ𝜔𝑑𝑡

𝜔1/2 𝑅𝐿−Δ𝜔]V +I𝑓−𝜔1/2 𝑡
𝑚

(1)

where
V𝑡 = [Re (𝑉𝑡 )],Im (𝑉𝑡 )I𝑓 = [Re (𝐼𝑓 )]Im (𝐼𝑓 )(2)

are the transmitted voltage and forward current, respectively.
The half-bandwidth 𝜔1/2 , coupling factor 𝑚, and loaded
cavity resistance 𝑅𝐿 are all parameters of the cavity itself,
and their relationship with the effective circuit model parameters can be found in [1] and [2]. The voltage reflectedby the cavity can be similarly computed [2] given a systemreference impedance 𝑍0 using the equation:
V𝑡 = [𝑍
1
Re (𝑉𝑡 )] = V𝑡 − 0 I𝑓
Im (𝑉𝑡 )𝑚
2(3)

RF Signal Chain
With an RF cavity model implemented, we then extended
the generator-to-cavity system used in [1] and [2] to include a number of additional hardware elements commonly
employed in RF systems. In order to properly simulate themuch more complicated propagation dynamics that can result from the addition of such elements, we chose to describe
incoming (a) and outgoing (b) RF waves at the ports of eachelement as power waves using a standard scattering matrix
approach [3] such that:
b=𝑆a

(4)

where the dimension of a, b, and 𝑆 are determined by the
number of ports on an element, and the elements of 𝑆 (thescattering matrix, are determined by the internal function of
the element. For example, the scattering matrix for an ideal
two-port RF transmission line (e.g., a coaxial cable or an RF
waveguide) of length 𝑙 is simply:
0
𝑆𝐿𝑖𝑛𝑒 = [ −(𝛼+𝑖𝛽) 𝑙𝑒𝑒−(𝛼+𝑖𝛽) 𝑙
0

]

(5)

where 𝛼 and 𝛽 are the typical attenuation and propagation
constants of the waveguide. The scattering matrix for someelements, such as the four-port “magic tee” signal splitter,can be derived geometrically:
MOPB101
259

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AN RF SIMULATOR FOR CONTROL SYSTEM DEVELOPMENT

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-MOPB102

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

LLRF AND PULSE-TO-PULSE CORRECTION FOR A COMPACT LINAC∗
J. Einstein-Curtis† , J. Edelen, M. Kilpatrick, RadiaSoft LLC, Boulder, CO, USA
R. Augustsson, R. Berry, A. Diego, S. Thielk
RadiaBeam Technologies, LLC, Santa Monica, CA, USA
B. Hong, Z. Li, C. Liu, J. Merrick, E. Nanni, L. Ruckman,
S. Tantawi, F. Zuo, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
Abstract
The advent of c-band and x-band technology has made it
possible to reduce the footprint of linear accelerators. Additionally, for industrial systems a more compact linac is anenabling technology for burgeoning applications in security
and defense. A key aspect to operating these machines in
an industrial environment is stabilization of the amplitude
and phase signals for the cavities. In this poster we present
the design and recent results for a LLRF and pulse-to-pulse
correction scheme utilizing an RFSoC based FPGA system.

INTRODUCTIONRadio-frequency (RF) particle accelerators rely on consistent and stable RF sources to operate in an optimal regime. In
particular, developers of industrial accelerators are looking
into ways to have higher RF power levels for more energetic beams, while also decreasing the system cost envelope.
Accomplishing both of these goals while maintaining a highquality beam over the entire flat-top of an accelerating pulse
is a significant challenge, requiring both a synchronizationof the timing and power systems involved in addition to active correction to account for system-wide variations due toequipment or environmental concerns.
It is essential to reduce the need for complex processing
algorithms when designing to minimize system cost whenmanufacturing at scale. We have developed a pulse-by-pulse
correction scheme that acts on system nonlinearities on aninter-pulse time frame. This algorithm is designed to generate a stable and flat forward power signal, using this signal
as an analogue for cavity voltage. Although our reported
method has limitations due to the lack of intra-pulse correction, it allows for a simple correction scheme without
requiring high-performance, low-latency hardware close to
the accelerating structure, increasing system complexity andcost. The correction algorithm has been developed to workin any EPICS [1] environment where the RF waveform isavailable as an EPICS process variable.
We implemented this scheme using prototype hardware
consisting of an AMD Xilinx ZCU216 RF-SoC evaluation kit, a custom trigger board, and supporting RF hardware [2–4]. The software platform is built on a SLAC∗ This material is based upon work supported by the Defense Advanced

Research Projects Agency under Contract Numbers 140D0423C0006
and 140D0423C0007. The views, opinions, and/or findings expressed
are those of the author(s) and should not be interpreted as representing
the official views or policies of the Department of Defense or the U.S.
Government.
† joshec@radiasoft.net
MOPB102262

developed software platform known as rogue [5]. This
leads to complications with system design for an industrial
accelerator due to the need to minimize components, butalso allows for clear functional compartmentalization andopportunities for SWaP+C minimization.

SIMULATION
We developed a system RF simulator to minimize theneed for actual hardware testing time. The simulator wasused to test a variety of control algorithms, including PID
and Kalman filter methods. The simulator was originallydesigned without signal delays or certain types of nonlinearities, which allowed for better processing speed, and wasconnected to EPICS PVs to integrate with the controller
algorithm. The system has several unusual design features,
including every two cavities a feed and load, requiring theability to decouple individual cavity efeects from a minimal
number of readback signals.
Results from the inter-pulse PID method can be seen in
Fig. 1. Both the PID and Kalman filter controllers performed
successfully, with the Kalman filter results shown in Fig. 2.
These responses clearly show the ability for the algorithm,
with proper tuning, to generate a flat waverform from an
originally uneven waveform.

LOW-POWER TESTING
Initial testing with RF was performed using the RF-SoC
LLRF system along with a conditioning pre-amplifier, preklystron RF amplifier, and the cavity structure. We used
this testing to refine the calibration algorithms and startup
routine, determining a procedure for setting proper delays
and the corresponding window in the readback signal forcontroller operation. This testing turned out to have additional benefits as the high power system was unavailable
due to equipment failure or bunker availability several times
throughout the project. Figures 3 and 4 show the algorithm
actively stabilizing the forward power signal and the calculated drive waveform. The initial 5 counts of the generated
signal are not a part of the integral portion of the PID accumulator to avoid attempting to correct for any effects resulting from RF or klystron turn-on. The end of the generated
waveform also shows the resultant effect due to amplifier
turn-off. Note the misalignment in time between the measured forward amplitude and generated drive waveform.
MOPB: Monday Poster Session
MC4.4 Low level RF32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUXA002

ESS INSTALLATION PROGRESSESDTL CONDITIONING HIGHLIGHTS

Abstract
The installation of the superconducting part of the ESS
Linac is progressing towards the first operation at 870 MeV
on the beam dump in January’25. A pilot installation of 1
spoke and 1 elliptical cryomodules was conducted in the superconducting (SCL) part of the ESS tunnel in spring 2023,
to practice the installation sequence as well as to complete
the cryogenic distribution system (CDS) commissioning.
Currently a total of 13 spoke and 14 elliptical cryomodules(9MB + 5HB) are being installed to allow 2 MW capabilities for the first phase of the project. Overall, 30 ellipticalcryomodules will be delivered to extend the power reach to5MW. At the time of the conference the linac will be in thetechnical commissioning phase.

INTRODUCTION
The European Spallation Source (ESS) in Lund, Sweden [1], is currently entering into the commissioning phase
after years of construction. The linear accelerator (linac)
will drive the most powerful neutron spallation source. The
linac is composed of both a normal and a superconducting
section, which will deliver an average ultimate beam powerof 5 MW at 2 GeV. The first and current phase intends todeliver a maximum power of 2 MW, followed by 3 MW in
2027. Figure 1 describes the layout of the linac as well as
the energy for the initial phase of operation.
The Normal Conducting Linac (NCL) section was completed in September 2023 with the installation of the fifth
Drift Tube Linac (DTL) tank. The DTL is delivered by the
Italian in-kind partner INFN. A section in this paper will
introduce some key parameters of the DTL as well as resultsof the conditioning up to DTL-4.
Regarding the Superconducting Linac (SCL) French inkind institutes contributed with three types of cryomodules(CM): spoke cryomodules from IJC Lab, Orsay, mediumbeta elliptical (MB) and high-beta elliptical (HB) cryomodules from CEA Saclay. All cryomodules must undergo Site
Acceptance Test (SAT) prior to their installation in the ESS
tunnel. The spoke CM were tested at FREIA laboratory in
Uppsala, Sweden. The elliptical CM on the other hand aretested in the Test Stand 2 (TS2) at ESS.
At the time of the conference, all 13 spoke, 9 MB and 5
HB (out of 21) cryomodules are installed in the linac. The
installation of the last systems and technical commissioning
phases are now overlapping in order to start the cooldownof the entire linac by October’24.
This paper will highlight some achievements in the NCL
and relate some key installation and commissioning processes in the SCL.

The ≈ 38.8 m ESS DTL is designed to accelerate the proton beam from 3.62 MeV up to 89.8 MeV. The five cavities
are now fully installed and tested in the linac tunnel. Moreover, in 2023 DTL-1 to DTL-4 were RF conditioned to fullpower and beam commissioned with maximum peak current at short pulses. From the SCL installation perspective,
the NCL conditioning could happen thanks to a 2 m thickconcrete wall separating the two areas.
The DTL-1 experience allowed significant enhancementof the field quality and the conditioning time of the next
cavities. Results and improvements regarding low power
field tuning [2] and RF conditioning strategy are presented
at this conference.
The automated conditioning of the DTLs starts at 10 µs-10 kW-1 Hz, stepping up to full power in the cavities at
3.2 ms -≈1.2 MW-14 Hz. The 4 DTLs reached the nominal
field and duty cycle (𝑃𝑎𝑣𝑒 ≈ 60𝑘𝑊) in March’23, including
long stability run with more the 95% RF ON over 12 hours.
The RF parameters measured at low power were then confirmed at high power. The RF pick-ups of the DTLs present acalibration error of ±5%, as expected from the measurement
error propagation of the attenuation. More details can befound in Refs. [3, 4].
During the last beam commissioning campaign in 2023,
the milestone of transporting and accelerate a 50 µs beampulse at nominal current to the end of DTL-4 was achieved.
Phase scan, longitudinal acceptance measurements, beamloading based measurements were used to find the correct
RF amplitude and phase set point of the four DTLs. The
results of those methods are in good agreement, with some
optimisation to be done in the next commissioning phases [4,5].
In September’23, after completing the beam commissioning at 74 MeV and the removal of the concrete wall, the last
DTL tank (DTL-5) was installed in the tunnel (Fig. 1). After the conclusion of the high power tests, the RF windows
and power couplers were assembled in May’24 [4]. The
DTL-5 is now connected to the rest of the subsystems andready for the integrated tests scheduled before high power
conditioning in November’24.

SCL INSTALLATIONThis section will present the spoke and elliptical CM
preparation and installation in the ESS tunnel as well as thefirst integrated tests performed on the water cooling systems.

CM Installation∗ henry.przybilski@ess.eu

The recent activities regarding the CM pilot installationof 1 spoke CM and 1 MB, and the CM preparation were presented at both SRF’23 [6] and IPAC’24 [7, 8]. The purposeof the pilot installation in Q2-2023 was to demonstrate the

TUXA: Main Session TUXTUXA002

MC3.4 Proton linac projects

265

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H. Przybilski∗ , on behalf of the European Spallation Source ERIC

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUXA004

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

FIRST TWO YEARS OF FRIB OPERATION*
P. N. Ostroumov† and J. Wei, on behalf of FRIB team
Facility for Rare Isotopes Beams, Michigan State University, East Lansing, MI, USA
Abstract
The Facility for Rare Isotope Beams (FRIB), a major nuclear physics facility for research with fast, stopped, andreaccelerated rare isotope beams, was successfully commissioned and has been in operation for the past two years.
Various ion beam species have been accelerated up to
300 MeV/u and delivered to the target. FRIB routinely provided 10 kW primary beams on target over the past year, afactor of 10 above used at the beginning of user operation.
Recently, a record-high 10.4 kW of uranium beam, themost challenging for accelerator systems, was delivered tothe target, and three new isotopes were discovered during
a short 24-hour run. We developed a 21.9-kW Se-82 beama month ago (in July 2024) and provided it for the first observation of neutron-rich rare isotopes. Every incremental
step in energy and power of primary beams allows us togain valuable experience in the facility's safe operation andprovides directions for further improvements. Several accelerator improvement projects are being pursued for further power ramp-up, improving the accelerator availability,
delivering more time for science, and preparing for the ultimate 400 kW beam on target.

INTRODUCTIONFRIB will provide access to 80% of all isotopes predicted to exist in nature. FRIB construction started in 2013
and was completed in 2022, on cost and ahead of schedule.
The FRIB facility is based on a heavy-ion CW superconducting driver linac, capable of accelerating uranium ionsto 200 MeV/u and higher energies for lighter ions with
400 kW power on target [1]. A detailed description of thelayout of the linac and beam commissioning results has
been presented in previous publications [1-4]. The linac
consists of A Front End (FE) composed of two Electron Cyclotron
Ion Sources (ECR), Low Energy Beam Transport(LEBT), Radiofrequency Quadrupole (RFQ) and Medium Energy Beam Transport (MEBT); Linac Segment 1 (LS1) containing 104 Superconducting (SC) Quarter Wave Resonators (QWR) and 39 SC
solenoids; Folding Segment 1 (FS1) containing a liquid lithium
charge stripper, an achromatic 180-degree bending
system, Charge Selection Slits (CSS) with the beamabsorber for unwanted charge states; Linac Segment 2 (LS2) containing 168 Half Wave
Resontaors (HWR) and 24 SC solenoids;___________________________________________* This material is based upon work supported by the U.S. Department ofEnergy, Office of Science, Office of Nuclear Physics and used resources of
the FRIB Operations, which is a DOE Office of Science User Facility under Award Number DE-SC0023633.
†ostroumo@frib.msu.edu
TUXA004
270

 Folding Segment 2 (FS2) containing an achromatic
180-degree bend; Linac Segment 3 (LS3) with 52 HWRs, 6 SC solenoids, and 80-meter beam transport; The Beam Delivery System (BDS) containing a 75deg achromatic bend and a final focusing system tocreate a 1-mm beam spot on the target.
In this paper, we report the results of ongoing developments to support experiments with various ion beam species and the beam power ramp-up up to 21.9 kW. We also
discuss Accelerator Improvement Projects (AIP) and R&D
initiatives to reach the ultimate beam power of 400 kW. To
date, the primary ion beams of 18O, 20Ne, 28Si, 36Ar, 40Ar,
48
Ca, 64Zn, 70Zn, 82Se, 86Kr, 124Xe, 198Pt, and 238U, at various
beam energies from 130 MeV/u up to 300 MeV/u havebeen delivered to the target and used to produce more than
270 unstable isotopes for 44 nuclear physics experiments.

OPERATIONAL EXPERIENCE
FRIB production runs for the science experiments commenced in May 2022. FRIB provided 4300 and 4200 hours
of beamtime in FY23 and FY24, respectively, with 94%
availability to support nuclear physics experiments [5].
About 25% of the beamtime goes to restoring, tuning, andstudies of primary beams. In addition, 2000 hours every
year are provided for Single Event Experiments (SEE) atbeam energies of various ion species from 10 to 40 MeV/u.
A total of 44 nuclear physics experiments have been conducted since the commencement of user operation. Oncethe development of primary and secondary beams is complete, the delivery of isotopes to the experiments has beenhighly stable. Some adjustments of the ECR were required,especially for metal beams, to maintain constant beam
power on target. The SRF cavities are operated at slightly
lower fields than the design to facilitate stable operationand provide a margin for quick recovery in the case of possible failure of some cavities. However, there has been no
cavity failure during the production runs in the past two
years. The Machine Protection System (MPS) operated as
expected [5, 6]. The lithium charge stripper contribution to
the facility downtime was dominant last year. Maintenanceon the Lithium Charge Stripper requires a significant
amount of thermal cool-down time before accessing thecontainment enclosure.

DEVELOPMENT OF ION BEAMS
Development of Linac Tune
The development of the linac tune for a new ion beam
starts with the pre-calculated setting of all beam optics devices and RF cavities for the entire linac. The RF cavities’
phases and amplitudes for any given ion species and its en-

TUXA: Main Session TUX
MC3.2 Ion linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

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SPIRAL2 OPERATIONS AND FUTURE PLANS
A. K. Orduz∗ , M. Di Giacomo, J-M. Lagniel, A. Leduc, G. Normand
Grand Accélérateur National d’Ions Lourds (GANIL), Caen, France
F. Bouly, A. Plaçais
Univ. Grenoble Alpes, CNRS, Grenoble IN2P3, LPSC-INP Grenoble, France
Abstract
GANIL (Grand Accélérateur National d’Ions Lourds)
started the operation of the SPIRAL2 superconducting linac
in 2022. Experiments in the Neutron For Science (NFS)
room, specific beam dynamics studies and different technical improvements are carried out during its operation in
the second half of each year, after the run of the cyclotrons
in the first half of the year. Up to now, accelerated particles are mainly D+ and 4 He2+ with energies between 7 and20 MeV/A. First linac tunings with 18 O6+ and 40 Ar14+ ion
beams at energies between 7 and 14.5 MeV/A were also
carried out to prepare the Super Separator Spectrometer (𝑆 3 )experimental area commissioning. The paper presents asummary of the beam time distribution during the second
year of operation, preliminary results of specific studies oncavity failure recovery and on pressure variation in the warm
linac sections induced by beam losses.

a selection of 1 bunch /100 using the Single Bunch Selector(SBS). For 13.5% of the total time used for machine studies,
6% was used for beam dynamics studies with 4 He2+ , 18 O6+
and 40 Ar14+ beams. Tests were performed on heavy-ion
acceleration at nominal energy and on linac operation incase of cavity failure, among others.

INTRODUCTION
The successful acceleration of the H+ , D+ and 4 He2+
beams to their nominal energies was performed during thelinac commissioning between 2019 and 2021 [1]. Thesebeams were also sent to the NFS room for initial tests andexperiments [2]. Since 2022, SPIRAL2 delivers beams forphysics experiments (mainly at NFS) and to carry out different studies on beam dynamics, diagnostics and others
accelerator systems. The beam dynamics studies performed
were mainly related to heavy-ion tunings for the Super Separator Spectrometer (𝑆 3 ) commissioning and to linac tunings
in case of cavity failure [3].
This article focuses on machine study results during thesecond year of SPIRAL2 operation. The first part presents
the 2023 operation timetable and the results of the first heavyion acceleration to 14.5 MeV/A. The second section describes the results of the acceleration of a 4 He2+ beam in
the linac in the case of cavity #6 failure. Finally, preliminary
results on the pressure variation in the linac warm sections
with heavy-ion beams are presented.

SPIRAL2 OPERATIONThe SPIRAL2 beam operation in 2023 was approximately
3 months from August 28 to November 19 (Fig. 1). Six
physics experiments and two main preparatory studies for
𝑆 3 were successfully conducted. The time for physics experiments represented 34.6% of which 83% was with D+ beams
between 9 and 47 µA mean intensity on target, mainly with∗ angie.orduz@ganil.fr

TUXA005
276

Figure 1: SPIRAL2 beam time sharing in 2023.
Heavy-ion beams 18 O6+ and 40 Ar14+ were tuned andaccelerated in 2022 up to 7 MeV/A, the energy requested by
𝑆 3 [4]. In 2023 a 50 µA 18 O6+ beam was tuned up to theproject nominal energy of 14.5 MeV/A (Fig. 2).
A power ramp-up to 2 kW with a 18 O6+ beam at
14.5 MeV/A was performed to qualify the tuning (Fig. 3).
The strategy was to accelerate the beam with a peak currentof 50 µA through the linac and to increase the pulse length
up to 100% duty cycle.

LINAC TUNING WITH A MISSING CAVITY
Since 2022, dedicated studies have been conducted on
linac operation in case of missing cavity. The procedure
started optimizing the linac parameters using TraceWin for a
specific missing cavity, then tuning the machine and finallyminimizing the beam losses. This last step is performed
slowly increasing the beam power and monitoring the diagnostics in the linac and HEBT [1]. In the case of a very firstlow 𝛽 cavity failure the debunching between two cavities is
so high that beam losses cannot be avoided. As the energy
increases the debunching decreases, so if one of the mid orlast low 𝛽 cavities fails, it is more or less easier to recover abeam dynamics without losses. To do so, one must retune
one or two upstream cavity and all downstream cavities torecover the required longitudinal acceptance, the price to
TUXA: Main Session TUX
MC1.1 Beam Dynamics, beam simulations, beam transport32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUAA002

Yuting Wu† , Andrei Ganshyn, Chris Compton, Ethan Metzgar, Kenji Saito, Kyle Elliott,
Laura Popielarski, Sang-hoon Kim, Spencer Combs, Taro Konomi, Ting Xu, Walter Hartung,Wei Chang, and Yoolim Cheon
Facility for Rare Isotope Beams - Michigan State University, East Lansing, USA
Abstract
A new surface treatment method is being developed, wetnitrogen doping, in which nitric acid is added during electropolishing (EP). In the first trial on a FRIB 𝛽 = 0.53 half-wave
resonator (HWR), a high quality factor (𝑄 0 = 8 × 1010 )was observed at 2 K at low field (accelerating gradient≤ 0.5 MV/m) without an anti-𝑄 slope. It is known that
the 𝑄 0 can be increased by shortening the mean free path
via surface contamination by oxygen. Low-temperature baking (LTB) can allow oxygen to diffuse into the surface to adepth similar to the RF penetration depth. However, nitrogencannot diffuse via LTB. Therefore, the mechanism for increasing 𝑄 0 with N-doping has not been clearly understood.
First results and analyses for HWR wet N-doping will bepresented.

of achieving similar results with simplified preparation steps.
This new recipe is called wet-nitrogen doping or EP (HNO3 );nitric acid is added to the traditional EP acid (a 10:1 mixtureof 98% sulfuric acid and 49% hydrofluoric acid). The goal
is to deliver nitrogen to the SRF surface during EP rather
than adding N-doping as an additional furnace treatment
step.
Wet doping was first developed by K. Saito and T. Higuchi
to mitigate hydrogen 𝑄-disease for mechanically-polishedand EP’ed cavities [3]. K. Saito recently revisited and foundthat the EP (HNO3 ) recipe can increase 𝑄 0 , as seen in Fig. 1.
EP (HNO3 ) was used to remove 50 µm, followed by LTB. A
high 𝑄 0 was seen up to 𝐸 𝑎𝑐𝑐 ≈ 20 MV/m with subsequent
HFQS, similar to results from furnace nitrogen doping [2].

INTRODUCTION
An effort is underway at FRIB to increase the quality factor (𝑄 0 ) and accelerating gradient (𝐸 𝑎𝑐𝑐 ) of superconducting radio-frequency (SRF) 𝛽 = 0.53 half-wave resonators(HWRs, 322 MHz), along with the production of a spare
HWR cryomodule for the FRIB linac. This effort is oriented
toward better accelerator maintainability and mitigation of
possible cavity performance degradation in long-term operation. Four objectives were identified: (1) Achieve higher
𝐸 𝑎𝑐𝑐 using electropolishing (EP) and low-temperature baking (LTB) in lieu of buffered chemical polishing (BCP);(2) Increase 𝑄 0 to ≥ 2 × 1010 at 𝐸 𝑎𝑐𝑐 = 12 MV/m by reducing the residual magnetostatic field; (3) Develop an EP
procedure with wet nitrogen doping; and (4) Develop a BCP
procedure without high field 𝑄-slope (HFQS). Objectives 1
and 2 were successfully completed in 2023; the results of
Objective 1 were reported at the last SRF Conference [1].
This paper reports on the first results of Objective 3.

MOTIVATIONA 𝑄 0 ≥ 3 × 1010 at 12 MV/m was reached in a FRIB
𝛽 = 0.53 HWR with EP, LTB, and remnant field reduction(Objective 2). However, efforts are ongoing to further improve 𝑄 0 . It is well-established that furnace nitrogen doping
can generate an anti-𝑄 slope for SRF cavities and thereby
increase 𝑄 0 at high field [2]. An alternative nitrogen doping
procedure is being studied for FRIB cavities, with the hope
∗ Work supported by the U.S. Department of Energy, Office of Science,

DE-S RC114424† wuyu@frib.msu.edu

Figure 1: Measured quality factor as a function of gradientfor EP’ed and wet-doped ILC-type cavities (1.3 GHz) at
KEK.

CAVITY PREPARATION AND COLD TESTCONDITIONS
For the initial tests, 120 µm was removed from the SRF
surface with wet doping EP. Three cold tests were performed
after wet doping: Test 1 was right after 120 µm removal andhigh pressure water rinsing; Test 2 was after LTB at 120◦
C for 48 hours; Test 3 was after an overnight 100 K “soak.”
LTB is effective to increase 𝑄 0 for FRIB EP’ed HWRs [1],which provided the impetus for Test 2. Since the SRF surface
should be mostly doped with nitrogen rather than oxygen,
and N does not diffuse at 120◦ C [4], we expect minimal
benefit from LTB. The 100 K soak tests whether hydrogenis present on the SRF surface to produce 𝑄-disease.
Additional tests were done after furnace hydrogen degassing and removal of an additional 25 µm with EP (HNO3 ).
Degassing is considered to reset the wet nitrogen doping,because nitrogen is also removed from the SRF surface, and

TUAA: Tuesday Oral Posters

TUAA002

MC4.8 Superconducting RF

279

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DEVELOPMENT OF WET NITROGEN DOPING TO IMPROVE THE
PERFORMANCE OF HALF-WAVE RESONATORS∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUAA003

A. Pisent, F. Grespan, C. Baltador, L. Bellan, M. Comunian, V. Conte, J. Esposito, L. Ferrari,
E. Fagotti, M. Montis, Y.K. Ong, A. Palmieri, A. Selva, INFN/LNL, Legnaro, Italy
P. Mereu, C. Mingioni, M. Nenni, E. Nicoletti, INFN sezione di Torino, Torino, Italy
A. Passarelli, M.R. Masullo, INFN sezione di Napoli, Napoli, Italy
V. Vercesi, S. Bortolussi1, INFN sezione di Pavia, Pavia, Italy1also Università degli studi di Pavia, Pavia, Italy
Abstract
The project Anthem, funded within the Next Generation
EU initiatives, foresees the realization of an innovative accelerator based BNCT (Boron Neutron Capture Therapy)
facility in Caserta, Italy.
The INFN (LNL, Pavia, Napoli, Torino) is in charge ofthe design and construction of the epithermal neutron
source, that will assure a flux of 109 s-1 cm-2 with characteristics suited for deep tumors treatment. The driver is a
cw RFQ, able to produce proton beam of 30 mA at 5 MeV.
impinging on a beryllium target. Specific challenges are related to the medical application of the device. In the paper
an overview of the project will be given.

INTRODUCTION
New neutron sources based on compact high intensity
linacs have recognized advantages respect to reactors andspallation sources for medical (and many other) applications.
One of the pilots of the project ANTHEM (AdvaNced
Technology for Human centEred Medicine) is aiming to
the realization of an intense source of epithermal neutrons
for Boron Neutron Capture Therapy (BNCT) for deepseated tumour treatment. Such neutron source is based ona high intensity linear accelerator under realization at
INFN (Istituto Nazionale di Fisica Nucleare), Legnaro National Laboratory, Pavia, Napoli and Torino units.

Figure 1: The RFQ integration on the new support.

TUAA: Tuesday Oral Posters
MC3.1 Industrial and medical accelerators

The accelerator is a Radio Frequency Quadrupole able
to accelerate 30 mA of protons up to 5 MeV. The RFQ(Figs. 1 and 2), together with the ion source TRIPS wasdeveloped in the last years in the framework of TRASCO
project at INFN LNL and LNS respectively.
The proton accelerator is coupled to a high-power beryllium target. For BNCT application this neutron source
promises unique performances in terms of neutron flux andspectra (very low gamma and fast neutrons components) as
needed for a successful therapy.
Table 1: ANTHEM BNCT Main Parameters
Ion source
Accelerator
Final energy
Beam current
Duty cycle
p-n Converter
Neutron source intensity
At BNCT port
RF power
Power consumption

MDIS
RFQ
5 MeV
30 mA
CW
Beryllium~1014 s-1
~109 s-1cm-2
1.0 MW~3.5 MVA

Proton energy 80 keV
352.2 MHz, 7.13 m longaccelerated
50% duty cycle possible
150 kW, 1kW/cm2
entire solid angle, Ave.
neutron energy 1.2MeV
epithermal

The proposal of a neutrons source based on TRASCO
RFQ for BNCT has a quite long history as SPES-BNCT [1]and MUNES projects [2]; for these R&D programs theconstruction of the facility was not funded, but many technological issues were solved.
Therefore, when in 2022 the group of physicists from
INFN, and the group of medical doctors and biologists
from Vanvitelli University met with the strong motivation
to build a BNCT facility, many elements were clear and a
successful proposal could be prepared in short time. Table
1 summarizes the main parameters of ANTHEM BNCT. In
this paper we shall concentrate in accelerator and target aspects.

Figure 2: The 3 RFQ segments at INFN-LNL.

TUAA003
283

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ANTHEM PROJECT, CONSTRUCTION OF A RFQ DRIVEN BNCTNEUTRON SOURCE

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUAA004

J. List ∗ 1,2 , W. Barth1,2,3 , C. Burandt1,2 , F. Dziuba1 , V. Gettmann1,2 , T. Kürzeder1,2 , R. Kalleicher1,2,3 ,S. Lauber 1,2 M. Miski-Oglu1,2 , H. Podlech4 , U. Scheeler1 , H. Vormann1 , S. Yaramyshev1,2
1
GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
2
HIM Helmholtz Institute Mainz, Mainz, Germany
3
KPH Johannes Gutenberg-University Mainz, Mainz, Germany
4
IAP Institut für Angewandte Physik, Frankfurt am Main, Germany
Abstract
The superconducting heavy ion HELmholtz LInear ACcelerator (HELIAC) is designed to meet the needs of theSuper Heavy Element (SHE) research and material scienceuser programs at GSI in Darmstadt. The beam energy can bevaried smoothly between 3.5 and 7.3 MeV/u, with an average
current of up to 1 mA and a duty cycle of 100 %. Recently
the first cryomodule CM1 was fully commissioned and tested.
CM1 comprises three Crossbar H-mode (CH)-type accelerating cavities, a CH-rebuncher, and two superconducting
solenoid lenses. Following the commissioning of the cryogenic supply- and RF-systems, a successful beam test was
conducted at the end of 2023. A Helium ion beam was
successfully accelerated to the design energy of 2.7 MeV/u.
The beam energy could be varied continuously between
1.3 MeV/u and 3.1 MeV/u without any significant particle
losses inside the cryomodule. In June 2024 a Argon ion
beam was accelerated to the design energy of 2.7 MeV/u.
This contribution covers the construction and commissioning of the first HELIAC cryomodule and the results of thebeam test campaign.

INTRODUCTION

0

1

1

2

2

Figure 1: Sketch of the HELIAC (top) and the first cryomodule (CM1), referred to as the Advanced Demonstrator(bottom).
To sustain and enhance the research programs in superheavy ions, material sciences, and biophysics at GSI
Helmholtz Centre for Heavy Ion Research (GSI), the superconducting (SC) heavy ion Helmholtz Linear Accelerator∗ j.list@gsi.de

TUAA: Tuesday Oral Posters
MC3.2 Ion linac projects(HELIAC) [1–4] is foreseen to be constructed on the GSI
campus. It will provide for continuous wave (CW) heavy
ion beams of smoothly variable energies between 3.5 and7.3 MeV/u with a mass to charge ration 𝐴/𝑍 between 1 and6. HELIAC comprises a normal conducting injector andthe SC main accelerator [2]. The injector consists of an
Electron Cyclotron Resonance Ion Source (ECR), a radio
frequency quadrupole (RFQ), and two alternating phase focusing (APF) interdigital H-mode (IH) cavities [5, 6] foracceleration up to 1.4 MeV/u. The SC part comprises four
separate cryomodules, each consisting of three SC crossbar
H-mode (CH) cavities [7–9] for beam acceleration, a SC rebuncher and two SC solenoid lenses with integrated steeringcoils, as well as two cold beam position monitors (BPMs).
Highlighted in Fig. 1 the first of the series HELIAC cryomodule CM1, (called Advanced Demonstrator) was assembled in the clean room of Helmholtz Institute Mainz (HIM),
transported to GSI and tested with a 4 He2+ and 40 Ar8+ beamprovided by the GSI High Charge State Injector (HLI) [10].

CRYOMODULE ASSEMBLY AND
INSTALLATION

Figure 2: Fully assembled cold string on rail system.
After the previous test of the first of series cavity CH0 in
2018 with beam [11], the cavity was transported back to HIM
to be assembled together with the remaining components ofthe coldstring of CM1 in the HIM clean room [12].
The assembly procedure of the cold-string components inthe clean room consists of an initial cleaning of all components in an ultrasonic bath, followed by a conductivity rinse.
The cavities are subjected to a high pressure rinse (HPR)
treatment at the manufacturer. Solenoids and bellows arecleaned with HPR in the clean room. After drying, the components are mounted on a trolley that runs on a rail system(Fig. 2). The cold part of the power couplers [13] are first asTUAA004
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BEAM COMMISSIONING OF THE FIRST HELIAC CRYOMODULE

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUAA005

I. J. Knight† , Georgia Institute of Technology, Atlanta, GA, USA
B. Mustapha, Argonne National Laboratory, Lemont, IL, USA
Abstract
In the field of accelerator physics, the quality of a particle
beam is a multifaceted concept, encompassing characteristics like energy, current, profile, and pulse duration. Amongthese, the emittance and Twiss parameters—defining the size,
shape, and orientation of the beam in phase space—serveas important indicators of beam quality. Prior studies haveshown that carefully calibrated statistical methods can extract emittance and Twiss parameters from pepper-pot emittance meter images. Our research aimed to retrieve theseparameters with machine learning (ML) from a transverse
image of the beam after its propagation through a pepper-pot
grid and subsequent contact with a scintillating plate. We
applied a Convolutional Neural Network (CNN) to extract
the x and y emittances and Twiss parameters (𝛼 and 𝛽), producing a six-dimensional output by simply looking at theimage without calibration information. The extraction ofdivergence-dependent parameters, such as 𝛼 and emittance,from a single image presented a challenge, resulting in alarge Symmetric Mean Absolute Percentage Error (SMAPE)
of 30%. To mitigate this issue, our novel method that incorporated image data from two points along the particles’
propagation path yielded promising results. 𝛽 prediction
achieved a low SMAPE of 10.5%, while 𝛼 and emittancepredictions were realized with a 16.5% SMAPE and 13.3%
SMAPE, respectively. Our findings suggest the potential
for improvement in ML beam quality assessment throughmulti-point image data analysis.

BACKGROUND

it placed transverse to the beam splitting it into beamlets.
In a PP emittance probe system, beamlets travel a short distance then hit a scintillating plate which fluoresces in thoselocations, see Fig. 1. An image of the plate is then captured
by a camera, see Fig. 2.

Figure 2: Real-world pepper pot image.
The beam envelope, the x and y extent of the beam, exist
in physical space; phase space is a theoretical space definedby the momentum and physical positions of particles in thebeam. Particles have position and momentum in three dimensions, for this reason there are 3 separate phase space
ellipses in the absence of coupling. The longitudinal coordinate, z, is the direction the beam travels, and the (x, y) planeor transverse plane contains the image that PP metering
captures.
𝛾𝑥 2 + 2𝛼𝑥𝑥 ′ + 𝛽𝑥 ′2 = 𝜖
where 𝑥 ′ and 𝑦′ represent momentum.
1+𝛼
=𝛾
𝛽

Figure 1: Pepper-pot emittance meter arrangement.
At the Argonne Tandem Linear Accelerator System (ATLAS), images of the beam are captured using a pepper-pot(PP) emittance probe. A pepper-pot is a plate with holes in∗ This work was supported by the U.S. Department of Energy, under Con-

tract No. DE-AC02-06CH11357. This research used the ATLAS facility,
which is a DOE Office of Nuclear Physics User Facility.
† ianknight@gatech.edu
TUAA: Tuesday Oral Posters
MC4.1 Beam diagnostics

(1)

(2)

The distribution of momenta and position of particles
when projected onto a phase plane generate an ellipse, referred to as the phase space ellipse. Twiss parameters(𝛼, 𝛽, 𝛾) and emittances (𝜖) define the size, shape, and orientation of the phase space ellipses as in Eq. (1). Beta is
proportional to the extent of the beam, horizontal or vertical,
in physical space. Emittance is the area of the phase space
ellipse, and in physical space, it relates to the spread of thebeam. Alpha is the correlation of position and momentum.
Visually, it describes the tilt of the beam in phase space.

Problem Definition
Our PP images, defined in physical space, do not fully
capture information about particles’ momenta as they show
a snapshot in time while momentum describes a process thatchanges over time. To extract the Twiss parameters fromTUAA005
291

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BEAM EMITTANCE AND TWISS PARAMETERS FROM PEPPER-POT
IMAGES USING PHYSICALLY INFORMED NEURAL NETS∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUAA006

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CRYOMODULE OPERATION EXPERIENCE FOR THE FRIBCONTINUOUS-WAVE SUPERCONDUCTING LINAC*
W. Chang†, Y.-L. Cheon, Y. Choi, X. Du, W. Hartung, S. Kim, T. Konomi, S. Kunjir, H. Nguyen,
K. Saito, Y. Wu, T. Xu, D. Zhang, S. Zhao
Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI, USA
Abstract
The superconducting (SC) driver linac for the Facility
for Rare Isotope Beams (FRIB) includes 46 cryomodules
for acceleration of heavy ions to 200 MeV/u. FRIB cryomodules have been supporting sustainable and reliable
delivery of high-power heavy ion beams, including 10 kW
uranium beams, to the target for production of rare isotopes
for user experiments in nuclear physics. The linac operates
in continuous-wave mode for maximum utilization ofbeam from the ion source. A total of 104 quarter-wave resonators (QWRs; β=0.041 and 0.085; 80.5 MHz) equippedwith stepper-motor frequency tuners and frictional mechanical dampers are operated at 4 K. A total of 220 halfwave resonators (HWRs; β=0.29 and 0.53; 322 MHz)equipped with pneumatic frequency tuners are operated at
2 K. We will present resonance control and phase stability
performance as well as experience with tuner systems inlinac operation. FRIB cavities are designed to be operated
at a peak surface electric field of approximately 30 MV/m.
We will present cavity field emission performance over theyears of linac operation and discuss field emission reduction measures such as pulsed RF conditioning (presently inuse) and plasma processing (in development). Automation
is a key aspect of efficient delivery of beams to users. We
will present our experience with automation of SC devices
such as start-up, shut-down, and fast recovery from an RF
trip as well as performance tracking of linac SC devices.

INTRODUCTION
The Facility for Rare Isotope Beams (FRIB) is a 400 kW
superconducting linac which accelerates stable ions up touranium to energies of ≥ 200 MeV/u [1]. The linac has afolded layout with 3 accelerating segments and 2 folding
segments, as shown in Fig. 1. The linac has a total 324
superconducting radio frequency (SRF) cavities and 69 superconducting (SC) solenoids. The quarter-wave resonators (QWRs) in Linac segment 1 (LS1) operate at 4.5 K;
the half-wave resonators (HWRs) in Linac Segment 2 and3 operate at 2 K; all SC solenoids operate at 4.5 K [2].
Beam is delivered to the target at full energy or to the
FRIB Single Event Effects (FSEE) experimental station
downstream of Segment 1. On 22 December 2023, the
FRIB linac reached a record high beam power of 10.4 kW___________________________________________*This work is supported by the U.S. Department of Energy, Office of
Science, Office of Nuclear Physics and used resources of the Facility for
Rare Isotope Beams (FRIB) Operations, which is a DOE Office of Science User Facility under Award Number DE-SC0023633.
†
chang@frib.msu.edu
TUAA006
294

Uranium with energy up to 177 MeV/u. The facility is currently delivered 10 kW primary beam power for users. An
increase in beam power to 20 kW is planned in 2024 [3].

Figure 1: Layout of the FRIB driver linac.

CRYOMODULE PERFORMANCE AND
IMPROVEMENTS
Cavity Field Level and Field Emission
Figure 2 shows the achievable average accelerating gradient (Eacc) for each cryomodule. Though some cavities
are operated at lower field, neighbouring cavities can operate at higher Eacc, such that the average gradients are above
the design goals.
Figure 3 shows the measured field emission (FE) X-rays
from the cavities. Compared with 3 years ago (FRIB cryomodule commissioning), a few cavities have stronger FE
X-rays. Conservative administrative limits are used tokeep the X-rays below ~10 mR/hr for most cavities to reduce the risk of further performance degradation. As a result, a few of the cavities are operated below their design
field, as mentioned above.

Figure 2: Average gradients in the FRIB cryomodules.

Figure 3: Field emission X-rays in the FRIB Linac.
High power pulsed RF conditioning and in-situ plasma
processing can reduce field emission. Several cavities improved after pulse conditioning [4]. Plasma processing has
TUAA: Tuesday Oral Posters
MC4.2 Cryomodules and cryogenics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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EVALUATION OF WAKEFIELD MITIGATION FOR UPGRADING THE
ATF FINAL FOCUS BEAMLINE
Y. Abe∗ , K. Kubo1 , N. Terunuma1 , T. Okugi1 , KEK, Tsukuba, Japan1
also at The Graduate University for Advanced Studies, SOKENDAI
Abstract
The KEK-ATF is an R&D facility for the final focus system to develop the nanometer beam technology required forthe International Linear Collider. The vertical beam size
growth as a function of the bunch intensity was observedat the virtual interaction point (IP), which is mainly caused
by wakefield. ATF is the best research environment for the
study of wakefield effects on the nanometer small beam.
The evaluation results of wakefield effects show that cavity
BPM and vacuum flange have strong effects on the small
beam. We are planning to upgrade the ATF-FF beamline to
reduce wakefield effects on the small beam. First, an internal
shield was inserted into the vacuum flange, one of the strong
wakefield sources, to evaluate the mitigation of the wakefield
effect. As a result, it was demonstrated that the wakefield
effect of the ICF70 flange can be mitigated by the RF shield
to the same level as that of a straight pipe.

impacts of the ICF70 flange, which is one of the strong wakefield sources, as a single component of the wakefield source
were experimentally evaluated. In addition, The wakefield
mitigation by inserting an internal RF shield into ICF70
flanges was confirmed. This paper reports the evaluation
results and the current status of the work to upgrade thebeamlines to reduce the effects of the wakefield.
Table 1: Nominal Beam Parameters for the Small Beam
Study
Parameter
Beam energy
Max. bunch population
Bunch length
Energy spread
Vertical emittance
Beta function at the IP

𝐸
𝑄
𝜎𝑧
𝜎𝐸
𝜀𝑦
𝛽𝑦

Unit

Value

GeV
109 𝑒− /bunchmm%
pm.rad
mm

1.3
20
7
0.08
12
0.1

INTRODUCTION
The KEK-ATF (Accelerator Test Facility) is an R&D facility for the final focus system to develop the nanometersmall beam (small beam) technology required for the International Linear Collider (ILC) [1]. ATF consists of LINAC,
Damping Ring (DR), Extraction (EXT) beamline and Final
Focus (FF) beamline [2, 3]. Figure 1 shows the layout of thebeamline after the DR. A low emittance beam is generated at
DR [4,5] and focused with the EXT and FF beamline to focus
the electron beam to 37 nm at the virtual interaction point(IP) [6]. Table 1 shows the nominal beam parameters for thenanometer small beam study. In 2016, it was confirmed thatthe vertical beam size at IP reached 41 nm [7].
Wakefield is an electromagnetic field generated by charged
particles passing through a structure in a beamline that has
geometrical shape changes. The excited wakefield acts as akick to the backward of the bunch, distorting its distribution.
It induces the bunch position change and the beam size
growth. It is important to study the wakefield effects on the
beam to develop advanced accelerators that require small
beam technology. ATF is the best research environment
for the detailed evaluation of wakefield effects on the small
beam because the nanometer small beam with low emittanceis generated, and the bunch center position and beam size
can be measured using high-precision monitors [8–10].
The vertical beam size growth as a function of the bunch
intensity at the IP has been observed at ATF, which is mainly
caused by wakefield. We are planning to upgrade the FF
beamline to mitigate wakefield effects on the small beam
by reducing the wakefield source from the beamline. The∗ abeyuki@post.kek.jp

TUAA007
298

IMPACTS OF EACH WAKEFIELD SOURCEON THE SMALL BEAM
Table 2 lists wakefield sources ( the vacuum components,
beam monitors, collimators, etc.) in EXT and FF beamlines and the amount of installations. The excited wakefieldon each wakefield source was calculated by GdfidL, which
is an electromagnetic field simulation code [11]. In addition, a new wakefield model was constructed to evaluate thewakefield effects on the small beam [12]. The impact ofeach wakefield source on the small beam caused by the orbit
fluctuation is expressed as 𝑊𝑦,𝑗 (𝑦 = 1mm, 𝑧) ∑𝑖 𝛽𝑦,𝑗,𝑖 [13]Figure 2 shows the evaluation result of wakefield effects on
the small beam of each type of wakefield source. It illustrated that cavity BPM and ICF70 flange have strong effects
on the small beam.

EVALUATION OF THE WAKEFIELDMITIGATION AS A SINGLE COMPONENTThe cross-section of the ICF70 flange is shown in Fig. 3.
We planned to insert a cylindrical RF shield made of stainlesssteel, as shown in Fig. 3, into the ICF70 flange to hide thegap. In this section, we described the evaluation resultsof the wakefield effects caused by the ICF70 flange on thesmall beam and mitigation by the RF shield. The effects
were evaluated by the orbit response method as a single
component of Wakefield source [14–16].
The effect of the wakefield kick caused by a single wakefield source on the beam can be quantified by the orbit response downstream from the wakefield source. This method
TUAA: Tuesday Oral Posters
MC1.1 Beam Dynamics, beam simulations, beam transport32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUAA009

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ON FORCED RF GENERATION OF CW MAGNETRONS FORSUPERCONDUCTING ACCELE RATORS*
G. Kazakevich#, R.P. Johnson, Muons, Inc., Newport News, VA, USA
T. Khabiboilline, G. Romanow, V. Yakovlev, Fermilab, Batavia, IL, USA
Ya. Derbenev, JLab, Newport News, VA, USA
Abstract
CW magnetrons, developed for industrial RF heaters,
were suggested to power superconducting RF (SRF) cavities of accelerators due to magnetrons higher efficiency
and lower cost comparing to traditionally used klystrons,
IOTs or solid-state amplifiers. CW magnetrons are regenerative RF generators with a huge regenerative gain. This
causes regenerative instability with a quite large noise. Traditionally CW magnetrons operate at the anode voltage
above the threshold of self-excitation. Stabilized by a small
injection-locking signal they were proposed to drive SRF
cavities. Then the magnetrons generate the injection locked
oscillations and generate noise. This may preclude use of
CW magnetrons in some SRF accelerators. We developed
described below a mode for forced RF generation of CW
magnetrons when the injected forcing signal provides startup and the regenerative noise is suppressed. The mode ismost suitable for powering high Q-factor SRF cavities.

INTRODUCTION
High-power CW magnetrons, designed and optimized
for industrial RF heaters, but driven by an injection-locking signal, were suggested in number of works to power
SRF cavities in accelerators due to higher efficiency andsignificantly lower cost of generated RF power per Wattthan traditionally used RF amplifiers (klystrons, IOTs,
solid-state amplifiers). The RF amplifiers driven by a master oscillator serve as coherent low noise RF sources. The
CW magnetrons are regenerative RF generators with ahuge regenerative gain of the resonant system to start up
reliably with a self-excitation by noise even if the tube ispowered by a DC power supply. Very large regenerative
gain causes a regenerative instability with a large level regenerative noise. Traditionally the magnetrons operate in
the self-excitation mode, i.e. with the anode voltage above
the self-excitation threshold, at a small injection-locking
signal, PLock ≈ -20 dBC or less of the magnetron power PMag.
In this case the regenerative noise of a CW magnetron violates a necessary correlation of the tube start up with its
injection-locking; the magnetron may be launched by thenoise or Power Supply (PS) ripples via side bands, but notby the injection-locking signal. Such probability is considered in the presented work. A novel method of forced RF
generation of CW magnetrons eliminating start up by noise
and PS ripples is briefly described below. The method was___________________________________________* Supported by scientific collaboration of Muona, Inc and Fermi National Accelerator Laboratory, Fermi Research Alliance, LLC under.CRADA-FRA-2023-0029.
#
e-mail: gkazakevitch@yahoo.com; grigory@muonsinc.com
TUAA009302

tested in experiments with CW magnetrons of microwave
ovens.

OPERATION OF A CW MAGNETRONINJECTION-LOCKED
BY A SMALL SIGNAL
We consider operation of a CW magnetron as it is traditionally assumed, in the self-excitation mode, at an injection-locking signal with low power PLock.
The effective bandwidth of injection-locking Δf, at thelocking signal is expressed by the following equation [1]:
Δf =

f0
2Q L

PLock
PMag

.
(1)
Here: f0 is the instantaneous magnetron frequency, QL is themagnetron loaded Q-factor, PMag is the magnetron output
power. For the 2.45 GHz, free running microwave ovenmagnetron type 2M137-IL the effective bandwidth ΔfFR
≈4.5 MHz [2]. Out of the effective bandwidth the magnetron cannot be injection-locked at the given PLock.
Then the probabilities of the injection-locking process
wLock and a free running operation wFR (PLock =0) for this2.45 GHz, CW tube one can estimate as:Δf
Δf − ΔfwLock ~
wFR ~ FRΔf FR , and
Δf FR
.
(2)
The probabilities estimates vs. PLock are shown in Table 1.
Table 1: The Values of wLock and wFR vs. PLock.
wLock
wFR
PLock
Δf,
-10 dB
3.87 MHz~0.86 ~0.14-20 dB
1.22 MHz~0.27 ~0.73-30 dB
0.39 MHz~0.09 ~0.91
Thus, probability of the injection-locked generation ofsuch RF source may be less than probability of the freerunning generation caused by noise. The noise oscillations
are much less in magnitude than the injection-locked ones.
Since the average time of motion of charges in the interaction space towards the anode is ~ f0-1<<QL/πf0 (the latter isa filling time of the magnetron resonant system), this results in a notable quasi-continuous noise spectrum. It is a
disadvantage for operation of the self-exciting magnetrons
with low locking signal for high Q-factor SRF cavities. The
distorted spectra of the RF sources with an intense quasicontinuous noise may preclude required suppression ofparasitic modulations (microphonics, etc.) and may increase the beam emittance in SRF accelerators.
Impact of power of the injection-locking signal on the
spectral density of noise power for the 2.45 GHz microwave oven free running magnetron plotted in Fig. 1 [3]TUAA: Tuesday Oral Posters
MC4.6 RF power sources and power couplers

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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PRELIMINARY MEASUREMENT OF 4D BEAM PHASE SPACE
DISTRIBUTION USING A SLIT EMITTANCE METER SYSTEM
S. Lee∗ , S.H. Moon, D.-H. Kim, H.-S. Kim, H.-J. Kwon
Korea Multipurpose Accelerator Complex,
Korea Atomic Energy Research Institute, Gyeongju, Korea
Abstract
Transverse emittances are generally measured in horizontal and vertical phase space separately as 2D projections of
4D phase space without any correlations between them. It istrue only if their degrees of freedom are independent. Recent
studies show that there exists correlation across conjugate
pairs. This correlation can affect beam dynamics and cause
beam loss. In our study, we sought to measure 4D beamphase space distribution with possible correlations. For thispurpose, we used a direct method of measuring the 4D phasespace distribution using slits. A set of 4 slits is used to slice
the beam into a specific volume of the 4D phase space, andthe charge inside each volume is measured. KOMAC has atest bench called BTS (Beam Test Stand) which consists ofa microwave ion source, LEBT, a 200 MHz RFQ and two
beamlines. At one of the beamlines, we have just installed
slit emittance meter system to measure 4D beam phase space
distribution. This paper presents our slit emittance metersystem and shows preliminary experimental results thereof.

INTRODUCTION
Beam diagnostics research for measuring high power
beam distribution becomes more important and is studied inseveral laboratories [1–4]. Especially in high power accelerators, nonlinear space charge forces cause beam loss which
can lead to radio-activation of the accelerator components.
It is important to understand the beam phase space distribution fully to reduce uncontrolled losses for the safe hands-on
maintenance. In this paper, we present works of measuring
4D beam phase space distribution specified below:• Slit emittance meter and its installation in BTS.
• Measurements of 4 D beam phase space distribution
with all possible correlations across conjugate pairs𝑥 − 𝑥 ′ , 𝑦 − 𝑦′ , 𝑥 − 𝑦′ , 𝑦 − 𝑥 ′ , 𝑥 − 𝑦 and 𝑥 ′ − 𝑦′ .
• Reconstruction of 𝑥, 𝑦, 𝑥−𝑥 ′ , 𝑦−𝑦′ , 𝑥−𝑦′ and 𝑦−𝑥 ′ beam
distributions from the 4 D phase space distribution
𝑓 (𝑥, 𝑥 ′ , 𝑦, 𝑦) measurement.
• Comparison between measured and reconstructed beam
distributions.
• Calculation of 4D emittance.

SLIT EMITTANCE METER
Slit emittance meter uses two pairs of slits installed at a
distance 𝐿 = 0.5 m. Fig. 1 (a) shows the cross-sectional viewof the chamber with a pair of vertical and horizontal slits.
∗ shl@kaeri.re.kr

TUAA010
306

These slits are driven by a set of linear motion manipulator and a stepper motor. The beam is directed to first slit
pair (slit 1 and 2 for 𝑥1 and 𝑦1 positions) and chopped into
flat beamlets. This beamlet is spread with initial angularspreads in x and y, and then passes through the second slit
pair (slit 3 and 4 for 𝑥2 and 𝑦2 positions). After passing
through all the slits, the final beamlet is measured as thebeam current at the collector. By repeating these measurements at various combinations of slit positions, the entire
phase space 𝑓 (𝑥, 𝑥’, 𝑦, 𝑦’) can be directly measured as 𝑥 = 𝑥1,
𝑦 = 𝑦1, 𝑥’ = (𝑥2 − 𝑥1)/𝐿 and 𝑦’ = (𝑦2 − 𝑦1)/𝐿. The slit
emittance meter is installed in the straight beamline of the
BTS. BTS consists of a microwave ion source, a LEBT (lowenergy beam transport) system, a RFQ (Radio Frequency
Quadrupole) accelerator, quadrupole magnets and beam diagnostics tools such as current transformer, faraday cups
and wire scanners as shown in Fig. 1 (b). The slit emittancemeter is installed as seen in Fig. 1 (c).

4D PHASE SPACE MEASUREMENT
The slit emittance meter installed in the BTS (Fig. 1 (c))
is set to measure multi-dimensional phase space distributions with certain combinations of slits. When measuringx’-y’, all 4 slits are used, which took more than 50 hourslong measurement time. And the 𝑥’ − 𝑦’ data can be used
to reconstruct its sub-dimensional distributions, that is, the𝑥 − 𝑥’, 𝑦 − 𝑦’, 𝑥 − 𝑦’ and 𝑦 − 𝑥’ distributions. In this section,
we show experimental results and compare directly measured distributions with distributions reconstructed fromx’-y’ data.

Measurements of Beam Phase Space Distribution
𝑥 − 𝑥’, 𝑦 − 𝑦’ and 𝑥 − 𝑦 beam phase space distributions aremeasured using the 𝑥1 − 𝑥2, 𝑦1 − 𝑦2 and 𝑥1 − 𝑦1 slit pairs
with the moving step of 0.5 mm respectively. For 𝑥 − 𝑦′ and𝑦 − 𝑥 ′ beam phase space measurements, we used three slits,
i.e. 𝑥1 − 𝑦1 − 𝑦2 and 𝑥1 − 𝑦1 − 𝑥2 pairs. For 𝑥 ′ − 𝑦′ beamphase space measurements, all four slits are used. These
measurement results are shown in Fig. 2 with phase space
ellipses (yellow dotted lines) of their emittances and twiss
parameters obtained from the beam phase distribution. The
emittance and twiss parameters are summarized in Table 1.

Reconstruction of Beam Phase Space Distribution𝑥 ′ − 𝑦′ measurement data is a function of beam intensitywith respect to 𝑥1, 𝑦1, 𝑥2 and 𝑦2 which can be written as,
𝐼(𝑥1, 𝑦1, 𝑥2, 𝑦2) = 𝐼(𝑥, 𝑦, 𝑥 ′ , 𝑦′ )(1)

TUAA: Tuesday Oral Posters
MC1.1 Beam Dynamics, beam simulations, beam transport32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUAA012

A. Oppelt†, N. Aftab, Z. Amirkhanyan, P. Boonpornprasert, D. Dmytriiev, J. D. Good, A. Grebinyk,
M. Gross, A. Hoffmann, L. Jachmann, D. Kalantaryan, W. Köhler, M. Krasilnikov, X. Li, Z. Lotfi,
F. Müller, S. Philipp, C.R. Richard, F. Riemer, F. Stephan, G. Vashchenko, S. Zeeshan
DESY, Zeuthen, Germany
D. Bazyl, M. Bousonville, F. Brinker, A. Ermakov, A. Jeromin, D. Lipka, C. Martens, L. Schaper,
S. Vilcins-Czvitkovits, DESY, Hamburg, Germany
X.-Y. Zhang, Tsinghua University, Beijing, China
Abstract
Gun5, the new generation of high-gradient normal conducting 1.3 GHz RF guns for linac-driven free-electron lasers like FLASH and European XFEL is under development at the Photo Injector Test facility at DESY in Zeuthen(PITZ). Its improved cell geometry and cooling concept allow for RF pulse durations of up to 1 ms at 10 Hz repetition
rate, at gradients of ~60 MV/m at the cathode. Gun5 is also
equipped with an RF probe for measurements of the RF
field inside the gun.
The first gun of this type, Gun5.1, is in operation at PITZ
since April 2022. Gun5.2 will be commissioned at the
FALCO conditioning facility at DESY in Hamburg, starting in June 2024. This gun is equipped with a balanced(symmetric) RF waveguide feed to the coaxial power coupler to prevent a coupler kick and thus improve the beam
quality delivered by the electron source.
Further guns are currently in the manufacturing process.
In parallel, studies towards a more reliable cathode spring
design are ongoing, in order to overcome observed issues
during the high duty cycle operation of Gun5.1. This article
will give an overview on all those developments.

INTRODUCTION
For 25 years, the development of electron sources forlinac-driven Free Electron Lasers (FELs) like FLASH andEuropean XFEL takes place at the Photo Injector Test Facility at DESY in Zeuthen. Over the years, the facility developed into a place for accelerator R&D, but the original
purpose of optimizing electron guns is still one pillar of the
PITZ research program.
The PITZ gun is an L-band (1.3 GHz) normal conducting 1 ½ cell standing wave copper cavity operated in πmode. In total,10 different electron sources (guns) havepassed through the PITZ facility over the years. During thistime, 5 optimized gun setups have been delivered to
FLASH, and 3 to European XFEL.
With time, the operations specifications for the electron
gun have changed towards more demanding parameters, interms of gradient and pulse length, as well as in terms ofstability and reliability. The currently envisaged operation
parameters are an RF pulse length of up to 1 ms at a repetition rate of 10 Hz, and an operation gradient of 60 MV/m,corresponding to an RF power input of up to 6.5 MW into
the gun cavity. At these parameters, the RF gun has to fulfill the user requirements in terms of stability and reliability.
TUAA: Tuesday Oral Posters
MC1.2 Electron and ion sources, guns, photo injectors, charge breeders

Gun5 is the latest generation of electron guns for highduty cycle operation with improved stability and reliability[1]. Compared to the previous Gun4 type, it has an optimized cell geometry with elliptical irises for higher RF efficiency and reduced surface field strength which shall allow for more stable and reliable operation. It furthermore
has an optimized water cooling which allows cooling of up
to ~65 kW average power. Thus, it permits higher duty cycle operation. Improved rigidity of the cavity will reducethe deformation over the up to 1 ms long RF pulse (pulse
heating). Another new feature is the existence of in-cavity
RF probe(s) which allow a direct control of the RF field in
the cavity and thus facilitate LLRF regulation. It furthermore allows the use of a new, symmetric RF distribution
system by means of a symmetric power coupler which has
the additional advantage of reducing the power load on theneeded RF windows by 50% by the use of two input arms.
Several cavities of Gun5 type are being produced and will
replace the currently used Gun4 type cavities at FLASH
and European XFEL.

GUN5.1
Gun5.1 is the prototype gun and is in operation at PITZ
since April 2022. It still uses the old RF distribution systemfrom the Gun4 type described in [2]. As reported in [2], theoperation of Gun5.1 at PITZ was limited by short interruptions within the first part of an RF pulse, so-called minibreakdowns, occurring at higher average power settings. In
2023, the gun conditioning focused on the study of thisphenomenon which was found to be related to a cathodespring problem that finally manifested in August 2023. The
cathode spring was therefore exchanged but the operation
stability did not improve significantly. Since the gun will
be exchanged in the near future, it was decided to finish theplanned physics program despite the instabilities, and to
use Gun5.1 afterwards as testbed for a new cathode springdevelopment, which is described below.

GUN5.2The design of Gun5.2 (and all subsequent guns) isslightly different from the prototype, Gun5.1. It has a reinforced cathode backplane, two pickups, and minimally corrected inner dimensions in order to better match the resonance frequency after production. The tuning parameters
are reported in Table 1 and compared to the values from
Gun5.1. The effect of correcting the inner cavity dimensions on the frequency after production is clearly visible.
TUAA012309

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STATUS OF THE L-BAND GUN DEVELOPMENT AT PITZ

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB001

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SMITH-PURCELL RADIATION STUDIES TOWARDS A COMPACT
HIGH-RESOLUTION LONGITUDINAL DIAGNOSTIC
B. Stacey∗ † , W. Kuropka, T. VinatierDeutsches Elektronen-Synchrotron DESY, Hamburg, Germany
W. Hillert
Universität Hamburg, Hamburg, Germany
Abstract
A new longitudinal diagnostic has been proposed, the
SPACEChip (Smith-Purcell ACcElerator Chip-based) diagnostic, which can infer information about the temporalprofile of a particle bunch from the Smith-Purcell radiation
spectrum generated when the bunch passes close to a dielectric grating. This is done using the bunch form factor after
retrieving the phase information. A simulated dielectric
grating has been excited by Floquet modes to investigate theangular distribution of the Smith-Purcell radiation. Progresson the SPACEChip experimental campaign at the ARES
linac at DESY will be reported, along with the expected
photon yield from the structure with the ARES operationalparameters.

When a charged particle bunch passes close to a periodic
change in refractive index, i.e. a grating of dielectric material, it is induced to radiate via the Smith-Purcell radiation(SPR) mechanism [1] as demonstrated in Fig. 1. The emis-

Figure 1: 3D model of SPR emission.
sion mechanism of SPR can be interpreted as the diffractionof the electron field [2]. SPR is spectrally dispersed andin-vacuum emission is governed by,(1)

where 𝛽 = 𝑣/𝑐 , 𝑣 is the velocity of the particle, 𝑐 is the speedof light in a vacuum, 𝜃 is the angle of emission, 𝑚 is thediffraction order, 𝜆 is the wavelength of the radiation, and𝜆𝑔 is the period of the grating. For 𝑚 ≠ 0, Eq. (1) describes
SPR of order 𝑚; for 𝑚 = 0, it describes Cherenkov radiation.
∗ also at Universität Hamburg, Hamburg, Germany† blae.stacey@desy.de

TUPB001
312

𝑑𝑃𝑚
𝑒𝐼𝑚2 𝐿=𝑑Ω
2𝜆2𝑔 𝜖0𝑠𝑖𝑛2 𝜃

− 𝑑1(𝛽− 𝑐𝑜𝑠𝜃)3|𝑅𝑚 |2 𝑒 ℎ𝑖𝑛𝑡 ,(2)

where 𝑒 is the elementary charge, 𝐼 is the beam current, 𝐿 is
the length of the grating, 𝜖0 is the permeability of free space,and 𝑑 is the impact parameter. |𝑅𝑚 |2 is the radiation coefficient, which is discussed in detail for metallic rectangularand volume strip gratings in [3, 4]. ℎ𝑖𝑛𝑡 is the interaction
length of the electron field virtual photons with the electron
bunch,
𝜆𝛽𝛾ℎ𝑖𝑛𝑡 =,(3)4𝜋
where 𝛾 = (1 − 𝛽2 )− /2 is the Lorentz factor. Equation (2)assumes that the radiation is emitted in the x-z plane, as
depicted in Fig. 1.
The use of SPR as a longitudinal bunch length diagnostic
is not a new concept, however previous work has mostly involved using metal gratings [5–8]. Here, dielectric gratings
are proposed, which can be produced with very high precision at low cost, due to advanced manufacturing techniquesin the computer industry.
The reconstruction of the longitudinal bunch current profile is done through the use of the form factor. The radiatedpower consists of incoherent radiation, 𝑆𝑖𝑛𝑐 which is proportional to the horizontal charge profile of the bunch, and coherent radiation, 𝑆𝑐𝑜ℎ , when the bunch length is shorter than𝜆𝑔 , which is proportional to the entire three-dimensional
current profile of the bunch. The total radiated power for abunch of 𝑁𝑒 electrons is,1

INTRODUCTION1𝑚𝜆− 𝑐𝑜𝑠(𝜃) =,𝛽𝜆𝑔

The power radiated per angle is described by the angular
distribution relation [2],

(

𝑑𝑃𝑚
𝑑𝑃
) = ( 𝑚 ) (𝑁𝑒 𝑆𝑖𝑛𝑐 + 𝑁𝑒2 𝑆𝑐𝑜ℎ (𝜔)),
𝑑Ω 𝑁𝑒
𝑑Ω 1

(4)

where the form factor for the coherent radiation, 𝑆𝑐𝑜ℎ , isgiven by,
− 𝑥

∞

2

𝑆𝑐𝑜ℎ = ∣∫ 𝑋𝑒 𝜆𝑒 𝑑𝑥∣ ∣∫
0

× ∣∫

∞

−∞

𝑇 𝑒−𝑖𝜔𝑡 𝑑𝑡∣

∞

−∞
2

𝑌 𝑒−𝑖𝑘𝑦𝑦 𝑑𝑦∣

2

(5)

,

where the charge distribution inside the bunch is assumed
to be 𝑞(𝑥, 𝑦, 𝑡) = 𝑋(𝑥)𝑌 (𝑦)𝑇 (𝑡), 𝜆𝑒 is the evanescent wavelength and represents the coupling efficiency between the
beam and the grating, 𝑘𝑦 is the 𝑦 component of the wave
vector, and 𝜔 is the frequency of the radiation.
TUPB: Tuesday Poster Session
MC4.1 Beam diagnostics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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LIMITATIONS OF THE EuXFEL 3RD HARMONIC CRYOMODULEIN HIGH DUTY CYCLE OPERATION
B. Richter∗ , A. Bellandi, J. Branlard, A. Heck, M. Herrmann, K. Kasprzak
Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
Abstract
Future High Duty Cycle (HDC) operation scenarios of
the European X-ray Free Electron Laser (EuXFEL) promise
increased bunch repetition rate and photon delivery, at thecost of changing system requirements and moving awayfrom the current mode of Short Pulse (SP) operation. To
assess whether the third harmonic cryomodule design is also
suitable for Long Pulse (LP) and Continuous Wave (CW)
operation, key parameters of the spare module are examined at the Accelerator Module Test Facility (AMTF). For
Radio-Frequency (RF) related energy efficiency, the cavity
resonance tuning precision and the loaded quality factor
tuning range are investigated. As performance indicators,
limitations on attainable cavity gradient and RF stability arequantified. The results show that the module in its current
design is insufficient for LP at high duty cycles and CW at therequired operating points. The installed 3-stub tuners only
yield maximum loaded quality factors between 5.3 × 106
and 1.9 × 107 , and the mechanical cavity tuner prohibits
tuning precision within the intended cavity half bandwidth.
Also, some higher order mode couplers do not allow CW
operation at required gradients. Nevertheless, closed-loop
RF stability measured in single cavity control is comparable
to that of the third harmonic system of EuXFEL.

INTRODUCTION
The European X-ray Free Electron Laser (EuXFEL) is a
hard X-ray light source for matter and technology research
providing the highest brilliance in the world. It is driven bya linear accelerator providing a bunched electron beam withenergies up to 17.3 GeV. Therefore, 800 superconducting
cavities are operated in Short Pulse (SP) operation modewith a Radio-Frequency (RF) flat top length of 650 µs at
10 Hz pulse repetition rate. Electron bunches are accelerated
during these flat tops at a repetition rate of up to 4.5 MHz.
To optimize bunch train utilization, a High Duty Cycle(HDC) upgrade of the linac allows to increase both the bunch
spacing and the number of bunches per second at the sametime. Different scenarios include substantially longer flat
tops of tens to hundreds of ms and reduced RF repetition
rates, called Long Pulse (LP), or even Continuous Wave
(CW) operation. However, such an upgrade demands careful
evaluation of required modifications to the machine.
Numerous R&D activities have been carried out since2007, mostly related to the cryomodules and periphery of
TESLA-type 1.3 GHz accelerating cavities. However, implications to the 3.9 GHz third harmonic system of the EuXFEL

were not investigated until 2017 [1], when the spare third
harmonic cryomodule X3M2 was assembled.
The main focus of this work is determining the limitations of the third harmonics cryomodule in its current statefor HDC operation. The resulting need for modifications
depends on the specifications of the target operating point,
which have not yet been decided.

CRYOMODULE X3M2
The third harmonic system at EuXFEL has been in operation since December 2015. It is used to linearize thelongitudinal beam phase space curvature induced by the firstaccelerating module in the injector section, enabling to maintain beam quality in subsequent bunch compressors and themain linac. In the current EuXFEL setup, the 8 cavities of
the cryomodule X3M1 are operated in vector sum, driven
by a single klystron.
In 2018, the third harmonic spare module X3M2 passed
the acceptance test for SP operation and has been installedin the Accelerator Module Test Facility (AMTF) since then.
All cavities achieved electric field strengths of 20 MV/mwithout field breakdown.
To assess whether the module is suitable for LP and CW
operation, the test bench was equipped with a 1 kW Solid
State Amplifier (SSA), ready for operation since March
2023. The system is set up in single cavity control configuration. However, the available infrastructure is limited
to provide 300 W drive power to the Fundamental Power
Couplers (FPC).

LIMITATIONS AND STABILITY
Efficient HDC operation requires changes to several interdependent parameters of the system:
Without beam, the obtainable gradient 𝐸cav depends on
the provided driving power 𝑃drive , the loaded quality factor
𝑄𝐿 , and the detuning Δ𝑓 from cavity RF resonance,√√ ( 𝑄𝑟 ) 𝑄𝐿 𝑃drive
𝐸cav =⋅√,
𝑙cav √
2𝑄 2
1 + (Δ𝑓 ⋅ 𝑓 𝐿 )gen⎷2where 𝑙cav is the cavity length, (𝑟/𝑄) the normalized cavity shunt impedance, and 𝑓gen the generator frequency. The
approach of reducing power demand through high loaded
quality factors thus requires precise resonance control, as
the impact of uncompensated disturbances on field stability increases. Besides, the maximum allowable gradient isbounded by the heat transport limit of the cryogenic system,∗ bozo.richter@desy.de

TUPB002
316

TUPB: Tuesday Poster Session
MC4.2 Cryomodules and cryogenics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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REACHING DESIGN ELECTRON ENERGY AT FLASHAFTER LINAC UPGRADE
V. Ayvazyan*, J. Branlard, C. Christou, K. Honkavaara, V. Katalev, D. Kostin,
J. Roensch-Schulenburg, L. Schaper, C. Schmidt, S. Schreiber, M. Wiencek, B. Yildirim
Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
Abstract
The FLASH 2020+ project at DESY includes, among
other modernizations, an increase of the electron beam energy. Two accelerator modules were replaced and the RF
distribution of other modules was optimized. The limiting
factors such as cavity breakdown and field emission wereidentified and measured through dedicated studies. At alater stage, based on these measurements, adjustments tothe high-power distribution were proposed and the optimal
operating point was demonstrated to achieve the design
electron energy of 1.35 GeV with the nominal RF pulse
length at FEL lasing conditions. After proper optimizationand tuning of the low-level RF parameters, the linac successfully operated at maximum energy and delivered FEL
radiation in the wavelength range below 3.2 nm. The measurement results as well as the achieved cavity gradientswith energy gains are presented.

INTRODUCTION
The FLASH [1] linac is based on TESLA superconducting RF technology and is built with accelerating modules(ACC) with eight superconducting RF cavities each. Currently seven ACC’s are installed in the linac. In 2022, during the first stage of the FLASH2020+ upgrade project [2],two accelerator modules were replaced and other modules
had their RF distribution scheme optimized to increase thebeam energy [3, 4]. The modules are powered either by a
5 MW or 10 MW (multi-beam) klystron. The cavities areoperating in a pulsed mode. The low-level RF system isused to maintain beam stability. An RF regulation systemprovides field control for the RF gun and for superconducting modules with the vector-sum group of cavities [5]. RF
power is distributed from a high-power klystron to the cavities via a forked set of waveguides. With the vector-sum
concept, one klystron powers a set of up to 16 cavities. The
synchronism of the incident waves to the cavities is ensured by waveguide tuners in front of each cavity whichallows phase adjustment for individual cavities. A frequency tuning mechanism (stepper motor and piezo) isused to operate the cavities on resonance. Each accelerating cavity has one input coupler for RF power and a pickup
antenna to measure the cavity field. The probes measure
the field directly inside the cavities. The measured fields
are digitized and further processed to calculate the vectorsum. After comparison with the set-point, a feedback correction is applied to the klystron drive. Standard operation
includes algorithms such as multiple input multiple outputbased feedback controller, adaptive feedforward and beamloading compensation.
___________________________________________* valeri.ayvazyan@desy.de
TUPB003320

NEW ACCELERATING MODULES
IN OPERATION
During the FLASH linac upgrade the two oldest andweakest accelerator modules (ACC2 and ACC3) were replaced by new ones with an adapted waveguide RF power
distribution and a new 10 MW klystron to feed 16 cavities.
The new modules were installed with a specially tailored
waveguide RF power distribution to achieve highest totalenergy for the new cavity gradient distribution. After installation, both modules were successfully tested withbeam at FLASH. The RF station could be operated providing an energy gain up to 465 MeV, with routine operation
between 400 and 460 MeV since October 2022. Prior tothis replacement, ACC2/3 was operated at a maximum
330 MeV energy gain. Therefore, the two refurbished modules significantly contributed to increasing the maximum
FLASH electron beam energy.

Achieved Gradients at ACC2/3
For high energy runs the confirmed operational gradientsfor ACC2 vary from 26.2 MV/m to 30.8 MV/m. The gradients variation at ACC3 are in a range of 23.3 MV/m to31.7 MV/m (Fig. 1).

Figure 1: ACC2/3 gradients (peak) at energy 460 MeV.
Modules are operated off-crest to allow beam compression.

RF DISTRIBUTION OPTIMIZATION FOROTHER MODULES
The original RF distribution scheme for ACC4/5 was linear. The klystron output RF power was equally distributed
among the cavities. Before the shutdown upgrade, the gradient hard limits (i.e. quench) were measured for each cavity. Figure 2 shows ACC4/5 gradient distribution before
shutdown. Based on these measurements, an RF waveguide distribution was tailored and assembled. After startup of the machine it turned out that the new dominating
limiting factor was field emission (gamma radiation) of
some cavities in ACC4. The investigations were carriedout under nominal RF pulse operation and the maximum
operational gradient limit as well as the limiting mechanism of individual cavities were determined. Either
TUPB: Tuesday Poster Session
MC4.4 Low level RF32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB005

Y. Sun∗ , A. Bellandi, J. Branlard, B. Richter, A. Eicher1 , C. Schmidt, H. Schlarb
Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
1
also at Hamburg University of Technology, TUHH, Germany
Abstract
Precisely calibrating superconducting Radio-Frequency(RF) linear accelerators is crucial for accurately assessing
cavity bandwidth and detuning, which provides valuable
insights into cavity performance, facilitates optimal accelerator operation, and enables effective fault detection anddiagnosis. In practice, however, calibration of RF signals
can present several challenges, with calibration drift beinga significant issue, especially in settings prone to humidity
and temperature fluctuations. In this paper, we delve into
the effect of environmental factors on the calibration driftof superconducting RF cavities. Specifically, we examine
long-term calibration drifts and explore how environmental
variables such as humidity, temperature, and environmental
noise affect this phenomenon. The results show that environmental factors, particularly relative humidity, significantly
influence calibration drifts. By analyzing these correlations,appropriate compensation algorithms can be designed to mitigate and eliminate these effects, thus optimizing calibration
accuracy and stability.

BACKGROUND
The European X-ray Free-Electron Laser (European
XFEL) is one of the most advanced facilities utilizing Superconducting Radio Frequency (SRF) technology, providing
researchers with unprecedented capabilities in probing thestructure and dynamics of matter at the atomic scale. The
European XFEL relies heavily on the stability and accuracyof the SRF cavities to ensure the high quality of the X-ray
pulses. Precisely calibrating RF cavities is crucial for accurately assessing cavity bandwidth and detuning, which
provides valuable insights into cavity performance, facilitating optimal accelerator operation.
A key challenge in the operation of SRF cavities is the phenomenon of calibration drift, which, if not managed properly,
can lead to significant performance degradation. Various
environmental parameters, such as temperature and humidity fluctuations, and mechanical vibrations, can influence
this drift, necessitating robust calibration and compensation
mechanisms.
The Low-Level RF (LLRF) control system plays a crucialrole in maintaining the stability of the RF fields within the
SRF cavities. The LLRF system continuously monitors andcontrols the RF signals to generate precise and stable RF
fields required for X-ray free-electron laser pulses, including
the compensation for any deviations caused by environmen∗ yue.sun@desy.de

TUPB: Tuesday Poster Session
MC4.4 Low level RF

tal factors. However, calibration drift remains a persistentissue despite the advanced control algorithms employed asthey rely on the calibration.
The Drift Compensation Module (DCM) [1] has beendeveloped as part of the LLRF system to address this challenge. It is specifically designed to mitigate the effects ofcalibration drift by dynamically adjusting the calibration
parameters in real-time. However, it is important to notethat DCM only calibrates the probe signal, not the drift offorward and reflected signals.
Accurate measurements of the RF forward 𝑉𝐹𝑚 and thereflected signals 𝑉𝑅𝑚 are critical for calculating cavity bandwidth and detuning. Ideally, the sum of 𝑉𝐹𝑚 and 𝑉𝑅𝑚 should
equal the RF probe signal 𝑉𝑃𝑚 . However, in practice, thefinite directivity of waveguide directional couplers and thedrift caused by environmental parameters impact the accuracy of the RF forward and reflected signals, thus degrading
the performance of the accelerator.
This paper investigates the long-term calibration drift insuperconducting RF cavities and examines the influence ofenvironmental factors on this phenomenon. By analyzing
the correlation between these variables, we found that thecalibration error or drift could be predicted based on environmental factors. Additionally, calibration coefficientscan be accurately forecasted, offering a promising calibration method for SRF cavities operating in Continuous Wave
(CW) mode.

RF SIGNAL CALIBRATION AND
CALIBRATION DRIFT
Long-term Calibration Drift
The original virtual probe is defined by the sum of themeasured forward 𝑉𝐹𝑚 ∈ ℂ and reflected 𝑉𝑅𝑚 ∈ ℂ RF
signals, expressed in In-phase and Quadrature (I&Q) formas
𝑉𝑃𝑣 = 𝑉𝐹𝑚 + 𝑉𝑅𝑚(1)
Ideally, the virtual probe 𝑉𝑃𝑣 should be equal to the measured RF probe signal 𝑉𝑃𝑚 ∈ ℂ. However, as mentioned
above, in practice, the finite directivity of waveguide directional couplers and drift due to environmental parameters
can affect the measurement of the RF forward and reflectedsignals, leading to calibration errors. Formally, calibration
error is defined as the difference between the measured probe
signal 𝑉𝑃𝑚 and the virtual probe 𝑉𝑃𝑣 , denoted as:
𝐸𝐶 = 𝑉𝑃𝑚 − 𝑉𝑃𝑣 = 𝑉𝑃𝑚 − (𝑉𝐹𝑚 + 𝑉𝑅𝑚 )(2)
TUPB005
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INFLUENCE OF ENVIRONMENTAL PARAMETERS ON CALIBRATIONDRIFT IN SUPERCONDUCTING RF CAVITIES

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB006

J. Wan† , A. Plastun, P. N. Ostroumov
Facility for Rare Isotope Beam, Michigan State University, East Lansing, MI, USA
Abstract
A machine learning-based virtual diagnostic approach forbunch length measurement is proposed. Utilizing multiple
measurements of bunch length at the Facility for Rare Isotope
Beams (FRIB) accelerator, a neural network model is trained
to learn the correlations between the spectra of the beam
position monitors’ (BPMs) signals and the bunch length.
This model enables rapid prediction of bunch length at BPM
locations without compromising beam quality.

and BPM 2278. Four superconducting bunching cavities
are installed upstream of those BPMs. The 80.5 MHz, 161
MHz, 241.5 MHz, and 322 MHz signal harmonics for those
BPMs are collected as input data of the machine learningmodel.

INTRODUCTION
The Facility for Rare Isotope Beams (FRIB) [1], operatedby Michigan State University, is a national user facility for advanced nuclear physics research. Since the commencementof user operation in May 2022 the primary beam power has
been steadily increased from 1 kW to 20 kW [2]. To ensure
the high-power beam delivery with no beam losses, accurate
measurement of the ion beam properties is crucial. For example, the bunch length measurements are very important for
matching stripped multiple charge-state beams and for optimizing the accelerator performance. Traditional instruments
for measuring the bunch length of ion beams are destructivesee, for example, Bunch Shape Monitor (BSM) [3]that caninterrupt the beam and also are not suitable for continuous
monitoring.
To address this challenge, a virtual diagnostic approachis proposed. This involves training a machine learning [4]model to learn the correlations between signals from nondestructive Beam Position Monitors (BPMs) and the longitudinal bunch length. While BPMs typically measure
the beam’s transverse position and phase, by analyzing thespectra of BPM signals, we can infer information about thelongitudinal properties. As a result, the model is expected to
predict bunch lengths at BPM locations in a non-destructive
manner.

DATA PREPARATION
Figure 1 shows the FRIB accelerator layout. Ion beams areaccelerated in the inner linac segment 1 (LS1), followed by
the folding segment 1 (FS1). A BSM is installed downstreamof the LS1, next to the charge strippers.
Five BPMs around the BSM are selected, which are defined as 2212, 2223, 2248, 2278, and 2313, according totheir locations. The BSM is installed between BPM 2248
∗ Work supported by the U.S. Department of Energy, Office of Science,

Office of Nuclear Physics, under Award Number DE-SC0024707 andused resources of the FRIB Operations, which is a DOE Office of Science
User Facility under Award Number DE-SC0023633.
† wan@frib.msu.edu
TUPB: Tuesday Poster Session
MC4.1 Beam diagnostics

Figure 1: Layout of the FRIB accelerator.
The goal of this project is to derive the bunch lengths at
the BPM locations from their signal spectra. Since direct
measurement at these locations is not feasible, we employ
simulation tools to estimate the bunch lengths by tracking
the ion beam from the superconducting bunching cavities
through FS1.
To determine the initial beam parameters in the simulation, we conducted a series of bunch length measurements
at the BSM location by varying the field strength of thecavities from 0 to 5.5 MV/m as shown in Fig. 2. With theaid of TRACK [5], a particle-in-cell (PIC) macroparticle
tracking code, the initial beam parameters are fitted by aParticle Swarm Optimization (PSO) [6] optimizer basedon the measured data. A resolution term 𝜎res representing
the uncertainties introduced by the BSM resolution is also
included in the fitting. The measured bunch length is determined by 𝜎measured = √𝜎2real + 𝜎2res , where 𝜎real is the real
bunch length.
Considering that the resolution of the BSM is comparablewith the RMS bunch length of the focused beam, resolutionrelated terms may compromise the precision of the measurements. To reduce the impact of this term, we opt to focus on
the geometric bunch length that covers 80% of the particles,
which is larger than the RMS bunch length by a factor of
2-3, depending on the beam phase space distribution.
It is important to note that for a Gaussian beam, the error
introduced by the BSM resolution tends to increase on the
80% geometric length, making this approach ineffective in
TUPB006
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MACHINE LEARNING-BASED NON-DESTRUCTIVE MEASUREMENT OF
BUNCH LENGTH AT FRIB∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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MACHINE LEARNING ENABLED MODEL PREDICTIVE CONTROL FOR
THE RESONANCE FREQUENCY OF THE FRIB RFQ∗
J. Wan† , S. Zhao, Y. Hao, W. Chang, H. Ao
Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI, USA
Abstract
Frequency detuning of the radio-frequency quadrupole(RFQ) at the Facility for Rare Isotope Beams (FRIB) is
managed by a cooling water control system. Efficiently
controlling the RFQ frequency remains challenging due tothe system’s time-delayed behavior. To address this, we
propose using a machine learning-based model predictive
control (MPC) approach. In this work, a long short-term
memory (LSTM) network is trained to project the variables
into a higher-dimensional space, and a Koopman network is
trained to predict the behavior of RFQ frequency detuning
given control actions. With the machine learning-based
MPC controller, the control time is expected to be reduced
by a factor of 2.

INTRODUCTION
The Facility for Rare Isotope Beams (FRIB) [1] is a user facility for nuclear physics research built at Michigan State University. The radio frequency quadrupole (RFQ) at FRIB is
designed to accelerate single and two-charge state ion beams
from 12 KeV/u to 0.5 MeV/u. To control the temperaturesensitive resonance frequency of the RFQ, a cooling water
system is designed to automatically control the temperatureof the RFQ with a proportional–integral–derivative (PID)
controller in case of the frequency detuning [2]. Due to thethermal process and the water transport delay, the control
process usually needs ten to twenty minutes to eliminate thefrequency detuning.
In this works, we propose to use a model predictive control(MPC) method based on a machine learning model to shorten
the control time. The machine learning model is a deep
Koopman network consisting of a long short-term memory(LSTM) neural network [3]. With the deep Koopman model,
we can obtain accurate predictions of the frequency behaviorof the RFQ, so as to apply it to MPC for better control
performance.

DEEP KOOPMAN NETWORK MODEL
The deep Koopman network, based on Koopman operator theory [4], has emerged as an innovative method ofpredicting the behavior of dynamical systems [5]. A deep
Koopman network aims to linearize the variable 𝑥𝑡 of a dynamical system to a higher-dimensional representation 𝜙𝑡using a neural network called encoder. The time-dependent
behaviour of 𝜙𝑡 can be described by a linear operator 𝒦.
∗ Work supported by the U.S. Department of Energy Office of Science

under Cooperative Agreement DE-SC0023633, the State of Michigan,
and Michigan State University.
† wan@frib.msu.edu
TUPB007330

By converting the variable from 𝜙 space to 𝑥 space withanother neural network called decoder, the behaviours of the
dynamical system can be predicted.
𝜙𝑡 = 𝜙(𝑥𝑡 )(1)

𝜙𝑡+1 = 𝒦𝜙𝑡 .

(2)

In this work, an LSTM network is selected to learn thetime-delayed information, including the temperature, pressure and flow of the cooling water related to the RFQ system(see Fig. 1). The linearized observable is then advanced witha linear operator 𝒦. To predict the behavior of the RFQ
frequency, a decoder is typically required to reconstruct the
RFQ frequency from the high-dimensional observable. However, in this work, we utilize a modified observable functionthat combines the time series of frequency 𝐹 with the original observable 𝜙. This structure eliminates the need for an
additional decoder, simplifying the prediction process.

Figure 1: Layout of the deep Kooman model. {𝑣0 , 𝑣1 , ..., 𝑣𝑛 }and {𝑢0 , 𝑢1 , ..., 𝑢𝑛 } represent the time-delayed data, where 𝑢
is the control variable. 𝜙𝑛 is a linerized observable function.
𝒦 represent the Koopman operator and 𝐹𝑛 is frequency
detuning at time 𝑛.

MODEL TRAINING AND EVALUATIONWith operational data from FRIB, a deep Koopman network is trained. The data is divided in two sets for training and testing purpose. As illustrated in Fig. 2, the model
demonstrates strong predictive capabilities on the test datafor both high detuning and low detuning scenarios. Thesefindings suggest that the model has successfully captured
the complex relationship between multiple input variables
and the RFQ frequency behavior.
It is important to note that certain variables, such as theforward power of the RFQ cavity, can strongly impact the
RFQ resonance frequency in a non-delayed manner. Thesevariables are generally stable and only occasionally experience rapid changes due to cavity trip or other accidents
during regular operations, which can cause substantial frequency detuning. It is observed that including these extreme
cases in the training is not always advantageous. Using that
extreme data in the training can lead to poorer performance
TUPB: Tuesday Poster Session
MC3.5 RFQs

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB009

A. D. Tran† , Y. Hao, Michigan State University, East Lansing, MI, USA
B. Mustapha, Argonne National Laboratory, Argonne, IL, USA
Abstract

Data Collection and Processing

Beam tomography is a method for reconstructing thehigher-dimensional beam from its lower-dimensional projections. This provides an understanding of the beam’s transverse phase space, enabling better modeling and predicting
downstream beam loss. We will show methods of extrapolating confidence intervals of our reconstructed beam andexplore a new beam tomography algorithms using Markov
Chain Monte Carlo (MCMC).

The data was collected over three days in November 2023,
and two primary data collection phases focused on beamemittance and beam tomography measurements. For the
first phase, a quadrupole scan was performed by varying
individual quadrupoles while keeping the others constant.
Data was collected by adjusting quadrupoles 6 and 7, as seenin Fig. 1 to measure the beam emittance.

INTRODUCTION
Beam tomography allows for the reconstruction of thebeam transverse phase space, which is very useful in optimizing accelerator performance, predicting and reducing
beam loss, and understanding beam behavior. It can aggregate existing beam measurement devices, which capture
projectional measurements of the beam, to reconstruct ahigher-dimensional beam phase space, such as the 4D transverse space (two positional and two momentum).
Current techniques for direct higher-dimension tomography in accelerators use algebraic reconstruction technique(ART) [1], machine learning (ML) [2], or maximum entropy technique (MENT) [3]. ART and MENT are limitedby computer memory, while ML requires a differentiable
simulation. However, it is efficient and not limited by memory. All of these methods need an accurate beamline model
to back-propagate projectional information about the beam,and not having this produces errors in the reconstruction.
This paper uses quad scans, simultaneous algebraic reconstruction technique (SART), and MCMC to arrive at
different conclusions about the initial beam phase space. We
will show a method to extrapolate a confidence interval using
SART, and showcase the limitations of MCMC as a potential
algorithm for fast approximation of the phase space.

METHODOLOGY
We will consider a linear system for our study and limit
our study to 4D. Beam tomography aims at retrieving thebeam distribution in phase space at location A, e.g., 𝑓 (X) =𝑓 (𝑥, 𝑥 ′ , 𝑦, 𝑦′ ) using the lower dimension measurement at location B, 𝑃(𝑥, 𝑦) or its projections. Let 𝑀(X, Q): ℝ4 → ℝ4
be the transfer map between A and B with Q = as the vectorof the accelerator tuning parameters such as the strength ofquadrupole. The beam will be assumed to be centered toignore the effect of offsets.
∗ This work was supported by a sub-award from Argonne National Labo-ratory and by the U.S. Department of Energy, under Contract No. DEAC02-06CH11357.
† tranant2@msu.edu
TUPB: Tuesday Poster Session
MC4.1 Beam diagnostics

Figure 1: A section of the ATLAS Beam Line.
Since the method of specifying desired beam settings
was unavailable, the beam settings were varied randomly.
The last four quadrupoles and two steerers were adjusted
within set bounds to manipulate the phase space sufficiently.
The aim was to maintain low beam loss since tomography
accuracy requires high accuracy and minimal beam loss.
This dataset was collected overnight to create set A. An
autoencoder-decoder analysis was employed on Set A togenerate alternative beam settings with high transmission.
While Set B successfully increased transmission, it did so
at the cost of reducing the angular range, which is needed
for accurate beam tomography reconstruction. An angularrange of 180 degrees is required for precise rebuilding, andthe reduced range in Set B, around 33∘ − 57∘ , limit thisaccuracy.
Various methods were used to filter and preprocess thedata for analysis. These involve filtering beam settings withover 100% transmission and those below 90% transmission.
Transmission over 100% is not possible and represent an error with the faraday cups while 90% was choosen to remove
settings with high beam loss. Projections were also fitted
to a gaussian curve with a vertical offset. The offset was
subtracted to establish a zero baseline, and an R-square score
was calculated to evaluate the fit. Data with an R-squared
score below 0.8 was discarded. The beam may also be offset
from the center, so a horizontal shift was applied to zero themean of the distributions. Due to different signal gains, theintegrated projections differ for each beam profile, so thesewere normalized to ensure consistency across projections.
Finally, to account for beam loss, the normalized projections
were scaled according to the transmission ratio, ensuringthat changes in beam transmission were accurately reflected.

Quad Scan
Quad scans [4] were performed to extract the beam emittances and sizes. Assuming this is an uncoupled system, letΣ0 be the beam matrix at the reconstructed location where
TUPB009
333

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TOMOGRAPHY DEVELOPMENT AT ATLAS∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB010

J. Brown† , T. Xu, Facility for Rare Isotope Beams, East Lansing, USA
D. Passarelli, G. Romanov, A. Sukhanov, Fermi National Accelerator Laboratory, Batavia, USA
Abstract
It has been found in benchmark tests that some Single
Spoke Resonator Type-2 (SSR2) cavities have early fieldemission onset as well as strong multipacting barriers. A
longstanding hypothesis is that field-emitted electrons in thehigh electric field accelerating gap can migrate and ignite
multipacting bands in the low electric field regions of thecavity periphery. In this study, we use simulation techniques
to examine multipacting behavior in SSR2 cavities fromelectrons seeded in common field emitter locations. Additionally, we investigated seed locations for areas in SSR2
cavities which may have poor coverage during high pressure
water rinsing and compared the multipacting behavior.

INTRODUCTION
Single spoke resonators have been used in numerous
projects to provide acceleration of hadrons and heavy ionsin the low to medium velocity regimes in accelerators [1].
The Proton Improvement Plan-II (PIP-II) at Fermi National
Accelerator Lab will be powered by a continuous-wave superconducting linac designed to accelerate H− ions up to
800 MeV [2]. PIP-II will utilize 35 SSR2 cavities to accelerate the ions from 35 MeV to 185 MeV [3]. The operational
fields from CST eigenmode solver and cavity geometry canbe seen in Fig. 1.

Figure 1: Electric and H-fields respectively for the 𝑓0 =325 MHz operational mode and accelerating electric field
amplitude of Eacc = 11.5 MV/m for SSR2.
SSR2 production and benchmark testing for PIP-II has
been ongoing. Early preliminary testing of SSR2 cavities has
shown strong field emission below 5 MV/m accompaniedwith stronger multipacting barriers [4, 5]. This work aims to∗ Funding agency: This manuscript has been authored by Fermi Research

Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S.
Department of Energy, Office of Science, Office of High Energy Physics.
This material is based upon work supported by the U.S Department ofEnergy, Office of Science, Office of Nuclear Physics under Award Number
DE-SC0018362.
† brownjac@frib.msu.edu
TUPB: Tuesday Poster Session
MC4.8 Superconducting RF

answer whether field emission can provide an explanation
for the increased multipacting strength and ignition.

SIMULATIONS
For this study, we utilized the particle-in-cell (PIC) andeigenmode solvers from CST Studio Suite. The eigenmodesolver is used to simulate the eigenmode electromagnetic
fields in SSR2 with the stored energy normalized to 1 J,
which are then exported to the PIC solver. An amplitude
parameter can be used in simulations to scale the eigenmode
fields and can be swept to examine particle behavior at different accelerating electric fields (Eacc ). Much of the modeland simulation setup for this study is based on previous studies for different prototypes of SSR2 and other cavities [6, 7].
The cavity walls have a secondary emission yield model for
Niobium that has been baked out at 300 °C from the CST
material library.
The PIC solver allows us to set the seed location andcharged particle characteristics. It is theorized that common
field emitter locations lie in the high electric field regions.
For SSR2 this is on the beam cup and iris areas along theinner conductor. Previous work has explored multipacting in
SSR2, from which we will be able to compare results fromdifferent seeds. Electron seeds previously used and our fieldemitter seeds can be seen on the cavity in Fig. 2.

Figure 2: a) Seed locations (in red) for previous simulation
work, which we will call global seeds. b) Field emitter
location seeds.
Our simulations run for 35 RF periods, which corresponds to ∼107 ns for SSR2’s operational frequency of
𝑓0 = 325 MHz. The number of emitter locations has a lower
bound due to the mesh, but to keep computation costs low,
64 emitter locations was chosen. The charge emission distribution in the PIC solver is natively set to Gaussian in time.
To keep the particles as close to discreet charges as possible, a large temporal standard deviation is used to obtain aflat distribution. A table containing the other distribution
settings can be seen in Table 1. Additionally, space charge
effect is accounted for in our simulations.
TUPB010337

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SIMULATIONS OF FIELD EMITTERS AND MULTIPACTING IN PIP-IISINGLE SPOKE RESONATOR TYPE-2∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA

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ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB011

FEASIBILITY STUDY FOR DUAL HIGHER-ORDER-MODES FOR
PLASMA PROCESSING OF FRIB SUPERCONDUCTING
COAXIAL RESONATORS ∗P. Tutt† , W. Chang, K. Elliot, W. Hartung, S-H Kim, T. Xu
Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI, USA
P. Berrutti, Brookhaven National Laboratory, Upton, NY, USA
Abstract

producing uneven coverage of the surface for plasma cleaning. One proposed solution is to use dual-driven higher-ordermodes (HOMs). Dual-mode excitation of plasma has been
demonstrated at ORNL and FNAL in multi-cell ellipticalcavities [4, 6]. In this paper, the feasibility of dual-driven
modes in FRIB’s 𝛽 = 0.085 QWR to promote better plasma
uniformity and sustain higher plasma densities will be explored.

In-situ plasma processing is a promising technique to reduce field emission in superconducting radio-frequency cavities and thus maintain maximum accelerator performancefor long-term operation. Continuous-wave accelerators such
as FRIB are more challenging than pulsed accelerators due
to relatively weak coupling (𝑄ext = 2E6 to 1E7 for FRIB)
via the fundamental power coupler (FPC). This results inan unfavorable mismatch at room temperature and makes
fundamental-mode plasma processing difficult. Hence wehave investigated the use of higher-order modes (HOMs)
with less FPC mismatch. Several HOMs are promising forlower-mismatch plasma generation. However, HOMs often
present a less favorable plasma distribution. To improve theplasma distribution, we are studying techniques to drive theplasma with two HOMs simultaneously. Plasma development results will be presented for FRIB 𝛽 = 0.085 quarterwave resonators including ignition threshold measurements
and plasma distribution assessments.

To drive 2 resonant modes in the cavity simultaneously,
the RF system was modified from the typical setup used at
FRIB [8]. The modified RF system is similar to the system used for dual-tone excitation of LCLS-II cavities at
FNAL [6]. The QWR’s tuning plate and bottom flange weremodified to add 2 viewports for a better view of the cavity
interior, as shown in Fig. 1. The extra viewports are alignedwith the accelerating gaps; a third viewport is installed on
one of the beam ports.

INTRODUCTIONHOMS FOR DUAL-TONE

Development of plasma processing, an in-situ method torecover performance degradation of superconducting radio
frequency (SRF) cavities, is underway at the Facility for
Rare Isotope Beams (FRIB). FRIB supports nuclear physics
experiments by providing heavy ion beams with energies up
to 200 MeV per nucleon using SRF quarter-wave resonators(QWRs) and half-wave resonators (HWRs) [1]. User operations at FRIB began in May 2022; potential future performance degradation of cryomodules is a concern [2]. Hence,in-situ methods for plasma processing of FRIB cavities arebeing developed. Several groups have investigated the effectiveness of plasma processing on SRF cavities [3–7]. Reductions in field emission after plasma processing have been
seen in several trials on FRIB cavities [8].
Recent plasma processing trials on the FRIB 𝛽 = 0.085
QWR have used HOMs for sustaining plasma due to theirimproved mismatch [8]. HOMs have the disadvantage ofmulti-lobed electric field distributions, with the plasma tending to ignite in only 1 of the lobes, resulting in a plasma
distribution that lacks the symmetry of the E-field, and hence

To determine what HOMs may be suitable for dual-tone,
CST Microwave Studio (MWS) [9] was used to simulate theelectromagnetic field distribution for HOMs up to twenty
times the accelerating mode frequency (80.5 MHz). Plasmameasurements were then done for modes with favorable field
distributions and coupling strengths.

∗ This material is based upon work supported by the U.S. Department ofEnergy, Office of Science, Office of Nuclear Physics and High Energy
Physics and used resources of the FRIB Operations, which is a DOE
Office of Science User Facility under Award Number DE-SC0023633
and DE-SC0018362.
† tutt@frib.msu.edu
TUPB011340

RF SYSTEM AND MODIFIED QWRFigure 1: FRIB 𝛽 = 0.085 QWR with modified tuning plate(left) and bottom flange (right).

MWS Simulation
The QWR was simulated with the FPC in its nominal
position at room temperature. HOMs were sorted according
to their coupling strength, field distribution, and maximum
field on the coupler tip (CT). Results for interesting HOMs
are shown in Table 1. Coupling strength and maximum field
TUPB: Tuesday Poster Session
MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA

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ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB012

ANOMALOUS FREQUENCY SHIFTS NEAR TC OF FUNDAMENTAL
AND HIGHER-ORDER MODES IN MEDIUM-VELOCITY
644 MHz SUPERCONDUCTING ELLIPTICAL CAVITIES*
S. M. Moskaitis, Y.-L. Cheon, S. Kim, P. N. Ostroumov
Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI, USA
Abstract
Recent studies indicate the magnitude of an anomalous
decrease in the resonant frequency, so-called frequency
dip, near critical temperature of superconducting niobium
cavities, Tc, correlates to the cavity quality factor, Q0, andimpurities introduced into the superconducting niobium
surfaces, such as nitrogen or oxygen. We measured frequency dips in both 644 MHz fundamental mode (FM) and1.45 GHz higher-order mode (HOM) of single-cell elliptical cavities for FRIB energy upgrade (FRIB400) R&D.
These measurements were performed in cavities with thefollowing surface treatments: (1) electropolished (EP)
only, (2) nitrogen-doped (N-doping), and (3) medium-temperature (mid-T) baked and then hydrofluoric (HF) acidrinsed. We will present measured frequency dips and compare them to cavity Q0 performance in the FM. Frequencydependent behavior of frequency dips with various surface
treatments will also be discussed as our experimental setup
has a unique feature compared to previous studies, whichallows for measurement of frequency dips in different
modes within the same cavity, in other word, on the same
surfaces.

INTRODUCTION
Recent study of bulk superconducting radiofrequency(SRF) niobium cavities has shown a relation between resonant frequency, frequency dip magnitude (denoted |fdip|),
and anti-Q slope [1].
These relations previously found between resonant frequency, |fdip|, and anti-Q slope are of particular interest in
the FRIB400 project. This project aims for Q0 = 2*1010 at
the accelerating gradient Eacc of 17.5 MV/m, operated at
2 K. The study of |fdip| and its cavity-to-cavity behavior
could give directions towards producing a 644 MHz 5-cell
elliptical cavity for the FRIB400 with lower BCS resistance at the operating Eacc, possibly through the realization of anti-Q slope in these 644 MHz cavities, which has
not been observed yet in mid-GHz frequency range cavities.

EXPERIMENTAL SETUP
We used three elliptical single-cell niobium SRF cavities
in our study. These single-cell cavities have resonant fre___________________________________________*This material is based upon work supported by the U.S. Department ofEnergy, Office of Science, Office of Nuclear Physics and High Energy
Physics and used resources of the FRIB Operations, which is a DOE Officeof Science User Facility under Award Number DE-SC0023633 and DESC0018362.
TUPB012344

quencies 644 MHz for their FM and 1.45 GHz for the selected HOM, TM020. These cavities all went through an
initial bulk EP, after which the treatment was specific toeach cavity. One cavity was nitrogen-doped at 800°C for 2
minutes at 25 mTorr and no annealing under vacuum at
800°C, so-called 2N0 doping, followed by post-doping 5
μm EP. Another cavity was baked at 330°C in the vacuum
furnace for 3 hours, followed by a hydrofluoric acid (HF)
rinse. The third cavity was simply left with its standard EP
as a baseline comparison. These cavities will be referred toas N-doping, mid-T Baking, and baseline EP, respectively.
The dual-mode frequency and temperature measurements of these cavities were performed using the following
steps. Lakeshore Cernox-1050 Resistance temperature detectors (RTDs) were placed on the cavity for temperature
measurements. The dunk dewar, in which one of the cavities was installed, was initially cooled down and liquid helium was accumulated at 4.5 K. We then pumped down the
dewar to 30 – 50 Torr, and started to warm up the cavity ata constant pressure. This is to eliminate the df/dp effectsuch that the measured frequency is solely a function oftemperature. A heater located at the bottom of the dunk
dewar was used to control the warm-up speed; we foundthat once the liquid level was below the cavity assembly,
the boil-off of liquid helium enhanced by the heater actually slowed down the cavity warm-up speed. With thistechnique, we could achieve the warm-up rate slower than
0.05 K/min at around Tc, which was useful to take precise
measurement of fdip.
We used two Vector Network Analysers to measure both
FM and HOM simultaneously. The FM was amplified up
to 3 – 5 W by a 644 MHz amplifier and driven to the cavity
through a standard high-power RF transmission line. On
the other hand, the HOM was driven via the reflected portof the bi-directional coupler in the RF transmission line.
The pickup RF signal was split by a 3-dB splitter and eachof them went to the FM/HOM VNA. We could detect almost the same RF power level between FM and HOM because coupling strength of both input and pickup couplers
is much higher in the HOM compared to the FM: S21 isapproximately 60 dB higher.
For each frequency dataset, the electron mean free pathof the cavity surface, 𝑙, was found by fitting the experimental data. To do this fitting, the experimental frequency
data was converted to penetration depth, λ(T), as represented by [2]:𝜆 𝑇 −𝜆 𝑇=⋅

𝑓 𝑇 −𝑓 𝑇,(1)

TUPB: Tuesday Poster Session
MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB013

Y.-L. Cheon† , S. Kim, W. Chang, W. Hartung, T. Xu
Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI, USA
Abstract
The superconducting radio-frequency (SRF) linear accelerator (linac) for the Facility for Rare Isotope Beams (FRIB)
has been operating for user experiments since May 2022,
using 104 quarter-wave resonators (80.5 MHz) and 220 halfwave resonators (322 MHz) operating with peak surface
electric fields (𝐸peak ) ranging from 27 MV/m to 33 MV/m.
Field emission (FE) can limit the maximum accelerating
gradients in SRF cavities and may worsen over time during long-term operation. RF pulse conditioning has beena useful technique to reduce FE in FRIB cryomodules forcommissioning and user operations. In this paper, we will
present RF pulse conditioning results and analysis for about
50 cavities, performed in cryomodule bunker tests and thelinac tunnel. During conditioning, we observe ”electricalbreakdown”, a rapid (<1 µs) collapse of the field, which usually leads to a significant reduction in FE X-rays. On theother hand, when a thermal breakdown (∼ms decay time,
also known as quench) occurs, opportunities for further conditioning at higher field are limited and FE X-rays may not
be significantly improved.

INTRODUCTION
Field-emitted electrons from the niobium surface of superconducting radio frequency (SRF) cavities are accelerated by the RF field and strike the cavity walls, generating
Bremsstrahlung X-rays. The emitters that generate the dominant field emission (FE) are likely located near the regionof the peak surface electric field (𝐸peak ), depending on thesurface cleanliness. The FE electrons and associated X-rays
can negatively impact the cavity performance by limiting
the maximum achievable accelerating gradient (𝐸acc ) or increasing the cryogenic heat load [1–3].
Field emission in FRIB cavities has been tracked and monitored during cavity Dewar tests, cryomodule bunker test,
and linac beam commissioning [4]. In the Dewar certification tests, FE was significantly reduced in a number ofcavities by repeating preparation steps (”FE reworks”) suchas ultrasonic cleaning, high pressure rinsing, acid etching,and mechanical polishing [5, 6]. These FE reworks could
be done relatively easily at the cavity certification stage, incontrast to the cryomodule test stage. On the other hand, RFpulse conditioning was found to be useful to mitigate FE in
FRIB cryomodules. Pulse conditioning in the cryomodule is∗ Work supported by the U.S. Department of Energy, Office of Science,

Office of Nuclear Physics and used resources of the FRIB Operations,which is a DOE Office of Science User Facility under Award Number
DE-SC0023633.
† cheon@frib.msu.edu
TUPB: Tuesday Poster Session
MC4.8 Superconducting RF

facilitated by the over-coupled fundamental power coupler(FPC), which is in contrast the matched couplers used for
Dewar tests. A statistical analysis of RF pulse conditioning
effects on the FE performance of FRIB cryomodules will be
discussed in this paper.

PULSE CONDITIONING
In bunker cryomodule tests and in-tunnel cryomodule
tests, we first measured FE X-rays as a function of 𝐸acc
in continuous wave (CW) mode, and then attempted pulse
conditioning if significant X-rays were produced below theoperating gradients. Pulse lengths of 30 to 50 ms were used(the RF fill time being a few tens of ms), with repetition rateof 1 Hz.

Electrical/Thermal Breakdown
Figure 1 shows the results of pulse conditioning in bunker
tests (Fig. 1(a)) and in the linac tunnel (Fig. 1(b)). Duringconditioning, we observed two types of rapid drops in thetransmitted RF power:• A rapid collapse in the field, faster than 1 µs, which weclassify ”electrical breakdown” (EB) [7].
• A decay taking of order 1 ms, due to ”thermal breakdown” (TB). This is faster than the normal decay dominated by the external quality factor of the FPC.
The FE onset field is significantly improved after EB, in
contrast to TB. This is consistent with EB theory [7, 8]: theemitter is heated by the field emission current, leading toa local increase in pressure of vacuum and exciting a local
discharge in which the emitter is explosively ”burned out.”
In TB, the emission current heats up the superconducting
niobium cavity surfaces, causing a quench (transition fromsuperconducting to normal conducting) before a local discharge can occur. This may explain why FE is not greatly
improved after TB. In TB cases, if we attempt a shorter pulse(closer to the fill time) with higher peak power, we do notsee a significant benefit. Generally, if pulse conditioning islimited by TB, it is difficult to induce EB after all.
The in-tunnel FE conditioning results (Fig. 1(b)) are divided into three cases: (1) during beam commissioning(2018-2021); (2) after user operation (2022-present); and(3) outliers in the statistical analysis such as non-conforming
cavities in bunker tests or one case of FPC cold cathodegauge failure [9]. The FE observed in the bunker tests islikely due mainly to particulate contamination during cryomodule assembly since, in most cases, the cavities did notshow significant field emission at the design field in the
TUPB013347

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RF PULSE CONDITIONING TO REDUCE FIELD EMISSIONIN FRIB SRF CRYOMODULES∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB015

Z. Yin†, W. Hartung, T. Konomi, S. Kim, T. Xu,
Facility for Rare Isotope Beams, East Lansing, MI, USA
J. W. Lewellen, Los Alamos National Laboratory, Los Alamos, NM, USA
J. Smedley, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
Abstract
Superconducting Radio Frequency (SRF) photo-injectors offer the possibility of producing low-emittance electron beams in continuous wave operation. Among the various photo-emissive materials, bi-alkali antimonide is favored for its high quantum efficiency (QE) at visible lightwavelengths. A development effort at FRIB is oriented toward the integration of advanced photo-cathodes into an
SRF photo-injector. This paper describes improvements tothe cathode preparation chamber, first cathode depositions,and characterization trials. A K2CsSb film was producedwith a notably extended dark lifetime, albeit with a modest
QE of approximately 2%. Extensive spectral response
analyses of the layer were conducted, along with thoroughassessments of measurement procedures and hardware.
This presentation offers insights into the factors contributing to the low measured QE and describes plans for improving the cathode preparation chamber and the experimental procedures.

INTRODUCTION
Electron beams with low emittance are vital for a wide
range of accelerator-based applications, including freeelectron lasers, Thomson scattering sources, and ultrafast
electron diffraction. Superconducting Radio Frequency(SRF) photo-injectors are particularly promising for generating low-emittance electron beams in continuous wave
(CW) operation [1].
In 2022, an SRF photo-injector system [2], including aphoto-cathode coating chamber, a 1.3 GHz 1.5-cell jacketed cavity, and a precise frequency tuner, was transferredfrom the High Energy Accelerator Research Organization(KEK) to the Facility for Rare Isotope Beams (FRIB). The
R&D focus at FRIB now includes the integration of innovative photo-cathodes within the SRF photo-injector
framework. Bi-alkali antimonide photo-cathodes, particularly K2CsSb, are attractive due to their high quantum efficiency (QE) in visible light [3]. These materials havedemonstrated QE of several percent with green light in various photo-injector laboratories [4-7], and notable longterm stability was observed in SRF photo-injector experiments at Brookhaven National Laboratory (BNL) in 2021
[7]. This paper discusses the development and experimental outcomes of photo-cathode materials, specificallydetailing the use of the photo-cathode chamber at FRIB for
deposition on niobium and P-type silicon substrates.

PHOTOCATHODE CHAMBER
The photocathode chamber serves two primary functions: (1) depositing the K2CsSb photocathode and(2) transferring the coated cathode to the SRF gun cavity
without contamination. In addition, it also allows measurement of cathode QE versus wavelength. Prior to coating, the cathode undergoes a heat cleaning at over 400°C
to eliminate residual gas and is then allowed to cool toroom temperature. A 10 nm layer of antimony (Sb) is deposited on the substrate heated to 130°C. The substratetemperature is then increased to 140°C for deposition ofpotassium (K) until the QE saturates at ~530 nm. Finally,
the substrate is cooled to 120°C for cesium (Cs) deposition
until the QE once again saturates. Essential equipment includes 3 evaporation sources, a thickness gauge, heaters,
temperature sensors, and a setup for real-time QE measurement.
An integrated load-lock system facilitates the safe transfer of the cathode to the SRF gun cavity under vacuum.
The photo-emissive film is susceptible to poisoning by residual gas, necessitating an ultra-high vacuum (UHV) environment (< 1e-8 Pa). This requires a full UHV system,
including a scroll pump, a 340 l/s turbo-molecular pump(TMP), a 300 l/s ion pump, and a 900 l/s(H2O) non-evaporable getter (NEG) pump. The layout is shown in Fig. 1.

Figure 1: Photocathode chamber drawings (left) and photograph of the as-built system (right).

___________________________________________* Work supported by MSU and the Department of Energy
Contract DE-AC02-76SF00515† yin@frib.msu.edu
TUPB: Tuesday Poster Session
MC1.2 Electron and ion sources, guns, photo injectors, charge breeders

TUPB015351

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DEVELOPMENT OF BI-ALKALI ANTIMONIDE PHOTOCATHODES FOR
A 1.3 GHZ SUPERCONDUCTING RF PHOTO-INJECTOR*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB019

M. Mayerhofer1 , G. Dollinger1 , R. Helm1 , J. Sonpar2 , H. Hähnel2
1 Bundeswehr University Munich, 85579 Neubiberg, Germany
2 Goethe University Frankfurt, 60438 Frankfurt am Main, Germany
Abstract
Additive Manufacturing (AM) has the potential to increase the performance of radio frequency (rf) cavity resonators while cutting manufacturing costs. To leverage thispotential, AM processes and potentially post-processing
techniques must be tailored to cavity requirements. Additionally, conventional manufacturing’s quality assurance
methods must adapt to the AM case requiring numerous studies on additively manufactured test bodies. We introduce acompact rf cavity design, enabling cost-effective and precise
studies of the surface conductivity of test bodies. The test
body is mounted on a dielectric holder inside a cylindrical
rf cavity made of aluminum. The geometry of the test bodycorresponds to a rod which allows simple and cost-effective
production, post-processing and evaluation. The test body’s
surface conductivity is extracted from a measurement of thequality factor (Q0 ) of the cavity. Depending on the geometryof the test body, Q0 values of over 10,000 can be achievedfor copper test bodies. Thereby, the test body is responsible
for up to two-thirds of the total cavity loss. Studies will bepresented demonstrating the precision of surface conductivity determination via Q-measurement and the impact of
uncertainties in test body position and geometry

INTRODUCTION
Conventional manufacturing of RF cavity resonators is expensive and design constraints limit performance [1,2]. Studies show that additive manufacturing (AM), especially Laser
Powder Bed Fusion (L-PBF), have the potential to produce
higher-performing cavities at lower costs [3–11]. For example, optimized cooling channels can improve cooling efficiency. However, after printing, AM cavities show higher surface roughness than conventionally manufactured ones, decreasing surface conductivity (𝜎𝑆 ). Current post-processing
techniques aim to reduce this roughness to achieve desired
quality factors (𝑄 0 ) [8, 11]. Nevertheless, predicting thesurface roughness-𝜎𝑆 relationship remains challenging, necessitating direct 𝑄 0 measurements on whole AM cavities
or cavities with AM manufactured complex internal geometries [3, 4, 8].
These geometries are time-consuming and expensive to
produce. Moreover, these complex geometries make it difficult to compare different post-processing methods and tocharacterize the part’s surface. We propose a test cavity setup
for rapid, precise 𝜎𝑆 evaluation on simple test bodies. The
symmetrical geometry of the test bodies allows uniform postprocessing and straightforward roughness analysis. Hence,
this setup enables an efficient comparison of post-processing
TUPB: Tuesday Poster Session
MC3.6 Room temperature structures

Figure 1: Test cavity a) mounted and connected to the VNA
and b) in individual parts
methods and an optimization of the RF cavity manufacturing
process without the need for complex and costly geometries.
A cost-effective and uniform generation of an empirical data
set can be achieved for the development of a Roughness-𝑄 0
methodology.

MATERIALS AND METHODSThe test cavity setup is shown in Fig. 1a. Two bolted
aluminum half-shells form the actual cavity. Each half-shellis equipped with an SMA connector for coupling of the rf
signal. The disassembled test cavity is shown in Fig. 1b. The
test body, mounted on a holder made of PTFE, is located in
the center of the test cavity. In this study, three test bodies
are examined: one made of oxygen-free copper annealedfor 3 hours at 530 ◦ C, one made of oxygen-free copper thatwas not annealed, and one additively manufactured from
TUPB019355

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A NOVEL TEST CAVITY SETUP FOR SURFACE CONDUCTIVITY
MEASUREMENTS OF ADDITIVE MANUFACTURING SAMPLES

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB020

H. Hähnel1† , B. Dedić, Institute of Applied Physics, Goethe University, Frankfurt a. M., Germany
1
also at Helmholtz Forschungsakademie Hessen für FAIR (HFHF), Frankfurt a. M., Germany
T. Torims, A. Ratkus, Riga Technical University, Riga, Latvia
M. Vedani, T. Romano, Politecnico di Milano, Italy
M.Vretenar, CERN, Geneva, Switzerland
M. Pozzi, Rösler Italian S.R.L, Concorezzo, Italy
E. Chyhyrynets, R. Caforio, C. Pira, INFN Laboratori Nazionali di Legnaro, Legnaro (PD), Italy
N. Kunkel, Technische Hochschule Mittelhessen (THM), Friedberg, Germany
Abstract
Significant progress towards the suitability of Additive
Manufacturing (AM) metal parts for the production of linear
accelerator components has been made in recent years. One
significant factor for the suitability of AM parts to produce
linac rf structures is the surface quality of the parts. Dueto the inherently higher surface roughness of AM metalparts, post-processing is necessary to reach surfaces suitable
for rf operation. We present most recent results of surface
post-processing trials with AM parts from stainless steel.

INTRODUCTION
Additive manufacturing (AM) of stainless steel and purecopper parts for the manufacturing of critical parts for linear particle accelerators is an interesting prospect for cost
reduction of these typically very complex structures [1–9].
First implementations of stainless steel parts use a oversize
print that is CNC machined and then copper plated with therest of the linac cavity [10–12]. The main benefit there is
the inclusion of complex cooling channels within the parts.
These implementations therefore still need very costly andtime consuming machining of the surface to achieve thedimensional accuracy and surface roughness needed. However, to fully harness the potential cost savings of metal AM,
this step should be eliminated. To reach this goal, we need
to identify surface finishing (polishing) processes, that can
produce parts with low surface roughness (𝑅𝑎 < 1 µm) while
maintaining the dimensional accuracy of the part or at least
show predictable mass removal of the part geometry.
In this paper, we summarize the current state of a study
to try to answer these questions for steel AM parts. To thisend, a small, cheap to print test geometry was developed
to evaluate as many geometrical scenarios as possible todifferentiate the different processes tested (see Fig. 1).
∗ Work supported by: BMBF 05P21RFRB2.

This project has received funding from the European Union’s Horizon
2020 Research and Innovation programme under grant agreement No
101004730 and is supported by the Latvian Council of Science under
grant agreement VPP-IZM-CERN-2022/1-0001.
Development of PEP technology financed from: PNRR MUR projectPE0000023-NQSTI.
† haehnel@iap.uni-frankfurt.de
TUPB: Tuesday Poster Session
MC3.6 Room temperature structures

TEST GEOMETRIESThe aforementioned test geometry is shown in Fig. 2,
where the purpose of the different features is noted. In
addition to different simple geometric features to stresstest surface finishing techniques, a short stem with a modified drift tube structure from an IH-DTL is positioned on
top of the part for evaluation of a more realistic scenario
as found in linac structures [3]. The test part measures
61 mm×20 mm×55 mm and is therefore more cost-effective
than printing full large linac geometries just for testing.
At this time, a total of 12 of these test samples have been
printed at the company Rosswag (samples 1–5) as well as
by colleagues at THM Friedberg with a focus on high partaccuracy (samples 6–12), as shown in Fig. 1. While samples
9–12 were not sandblasted (SB) after printing (see Fig. 3),
all other parts were sandblasted after printing to remove
residual powder from the parts surface.

Figure 1: Test geometries in sorting rack. Samples 11 and
12 are still unprocessed.

SURFACE FINISHING PROCESSES
Test samples were sent to different companies and researchers for surface finishing with different techniques. The
processes used for this study so far are summarized in Table 1.
The processes include two trials with vibratory mass finishing (PERS, Rösler), which is known to be able to produce
very smooth parts at higher processing times. One potential
TUPB020
359

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SURFACE FINISHING OF ADDITIVE MANUFACTURING PARTS
FOR PARTICLE ACCELERATORS ∗32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB021

H. Hähnel1,2∗ , A. Ateş1 , L. Bauer1 , B. Dedić1 , K. Kümpel1 ,C. Wagner1 , H. Podlech1,2 , U. Ratzinger1,2 , C. Zhang1,2,3
1
Institute of Applied Physics, Goethe University, Frankfurt, Germany
2
Helmholtz Forschungsakademie Hessen für FAIR (HFHF), Frankfurt, Germany
3
GSI Helmholtz Centre for Heavy Ion Research, Darmstadt, Germany
Abstract
The Frankfurt Neutron Source FRANZ will be a compact
accelerator driven neutron source utilizing the 7 Li(𝑝, 𝑛)7 Be
reaction with a 2 MeV proton beam. Followoing successful
beam commissioning of the 700 keV proton RFQ, further
beam experiments including emittance measurements are
currently ongoing. Preparations for conditioning and commissioning of the IH-DTL are running in parallel to thecurrent beam measurement campaign. We report on thecurrent status of commissioning towards a 2 MeV proton
beam.

RFQ RETROFIT
A change of the RFQ injection energy to 60 keV, necessitated a redesign of the RFQ electrodes. The new beam
dynamics design is base on the so-called SEGLER method
and the resulting electrode geometries were developed in
2022 [12, 13]. Production of the new electrodes was orderedin summer 2022. The RFQ retrofit and low level rf tuning
was finished in summer of 2023. Following that, rf conditioning and finally beam comissioning were performed.

INTRODUCTION
The Frankfurt Neutron Source (FRANZ) is a compact
accelerator driven facility originally initiated in the early
2000s [1–6]. It is designed to provide a 2 MeV proton beam
for neutron production via the 7 Li(𝑝, 𝑛)7 Be reaction [7]. The
produced neutrons with a thermal spectrum around 30 keV
can be used for a number of experiments in the fields ofapplied physics and experimental astrophysics [8].

Figure 1: Photograph of the current FRANZ LEBT beamline(Aug. 2022).
Significant progress on the driver linac was made recently.
The commissioning of the new CHORDIS ion source [9,10]
in late 2020 was a first milestone. Since the CHORDIS
ion source only provides a 35 keV proton beam, an electrostatic post-accelerator was developed and commissioned at
IAP to reach the desired beam energy of 60 keV [11]. After stable operation was confirmed, the Low Energy BeamTransport line (LEBT), see Fig. 1, was commissioned andthe beam was transported up to the point of injection into the
RFQ-Accelerator. The 60 keV beam is now in routine operation at the FRANZ. This presents an important milestone
for the initial beam commissioning of the FRANZ facility.
Meanwhile, emittance measurements to further improve an
efficient injection into the RFQ haven been performed.
∗ haehnel@iap.uni-frankfurt.de

TUPB: Tuesday Poster Session
MC3.6 Room temperature structures

Figure 2: FRANZ RFQ after installation of the new electrodes and successful delivery to IAP Frankfurt with the lid
open for final RF tuning.

RF TUNING
After the installation of the new RFQ electrodes at thecompany Neue Technologien GmbH (NTG) in Gelnhausen(see Fig. 2), the final RF tuning was performed on site incollaboration with IAP. A total of 18 tuning plates had to beinstalled and adjusted to tune the final frequency of 175 MHzof the RFQ while maintaining a flat voltage distribution
over the whole length of the RFQ. For the measurements,
the frequency shift introduced by a small dielectric plastic
cylinder placed on top of the electrodes is recorded at a
position above each tuning plate to deduce the flatness. This
process took about two days with numerous iterations, until
the results were satisfactory. The final field flatness waswithin ±3 % which is a typical acceptable value for a fourrod RFQ (see Fig. 3 (left)).
TUPB021363

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CURRENT STATUS OF BEAM COMMISSIONING
AT THE FRANKFURT NEUTRON SOURCE

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB022

J. D. Kaiser∗ † 1, 2 , A.Ateş1 , H. Hähnel 1, 2
1Institute of Applied Physics, Goethe University, Frankfurt a. M., Germany
2
Helmholtz Forschungsakademie Hessen for FAIR (HFHF), Frankfurt a. M., Germany
Abstract
Additive manufacturing (AM) has established itself as a
powerful tool for rapid prototyping and the production ofcomplex geometries. For use in a 433 MHz IH-DTL cavity,
a CF 40 coupler is being developed that is manufactured
from pure copper using a 3D printing process and has awater cooling concept that cannot be realized using conventional methods. The coupler consists of a ceramic window
which is cooled on both sides, an outer conductor with spiralcooling channels and a cooled inner conductor. Thanks to
its modular design, the individual components can be easily
replaced. The ideal transmission is frequency-dependent
and was adjusted by fine-tuning the inner conductor structure in CST-Simulations. A prototype made of aluminium
was built for verification purposes.

is tapered to reduce the radial capacitance between the innerand outer conductors. The coupler is composed of a totalof six individual parts. The components in the vacuum areproduced using additive manufacturing, while those on theatmosphere side are made conventionally, as they lack cooling channels within the solid material. The individual parts(see Fig. 2) were delivered at the beginning of August andare currently undergoing surface treatment and finishing in
the workshop.

COUPLER DESIGNFor high power testing of a 3D-printed IH cavity [1–3],
the coupler currently in use is to be replaced by a 3D-printed
coupler with full water cooling to withstand higher thermalloads. A Teflon vacuum window is currently in use and will
be replaced by a ceramic one in the form of a simple disk
(Degussit AL23 by Kyocera). As a result, the design has
been completely revised and adapted to the HF propertiesof the ceramic (see Fig. 1).

Figure 2: Raw parts before post-processing.

RF-Transmission Optimisation

Figure 1: Half section view of the advanced compact CF 40
coupler.
The ceramic is sealed with O-rings, enabling costeffective manufacturing and quick replacement of the window if damaged. To offset the additional capacitance causedby the separation of the inner and outer conductor sections
due to the ceramic, the outer radius of the inner conductor∗ kaiser@iap.uni-frankfurt.de† Work supported by BMBF 05P21RFRB2

TUPB: Tuesday Poster Session
MC3.2 Ion linac projects

Figure 3: Schematic representation of the internal geometryof the coupler with cone lengths A, B and offset ∆, which
are significant for the frequency setting.
The transmission line is composed of five sections (seeFig. 3). The input and output sections follow the standard
50 Ω coaxial geometries, while the middle section, which
includes the ceramic window, is shaped according to the
TUPB022367

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DEVELOPMENT OF A COMPACT RF COUPLER UTILIZINGADDITIVE MANUFACTURING

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB023

U. Ratzinger†, S. Altürk, H. Hoeltermann, Bevatech GmbH, Mörfelden-Walldorf, Germany
R. Cee, T. Haberer, A. Peters, Heidelberg Ionenstrahltherapie Centrum, Heidelberg, Germany
H. Hähnel, H. Podlech, C. Zhang, Goethe-Univ. Frankfurt, Frankfurt am Main, Germany
M. Schuett, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
Abstract
The tumor therapy facility HIT at Heidelberg is in operation with light ion beams up to carbon since 2006. The
7 A MeV, 216.8 MHz synchrotron injector linac with a total length of 5 m was designed for the ion C from an ECR
ion source. The RFQ accelerates the beam from 8 A keV
up to 400 A keV and is at present a bottleneck in beamtransmission. After a careful analysis of the beam quality
along the Low Energy Beam Transport system LEBT and
the RFQ it was decided by HIT to order a new RFQ from
Bevatech with higher beam acceptance and with tight mechanical tolerances. Other features are optimized entrance
and exit gaps by including longitudinal field components,
which are characteristic for 4-Rod-RFQs. A complete dipole compensation along the mini-vane electrodes is another improvement. This RFQ is scheduled to replace theold one in 2026.

RFQ BEAM DYNAMICS
The beam emittances at the end of the LEBT were measured and analysed carefully for all types of ion beams applied at HIT. It was then concluded, that the new RFQ will
be based on normalized rms emittances of 0. 25 mm mrad.
Higher RFQ acceptances would not pay off in the overall
performance of the injector linac due to the limitations
along the ITS and the IH-DTL, which will not be rebuilt.
For local technical reasons the total RFQ tank length was
limited to a maximum of 1492 mm. A view on the new
RFQ is shown by Fig. 1.

INTRODUCTION
The carbon therapy injector linac [1] was originally developed for the Heidelberg HIT facility and was reproduced for CNAO in Pavia, MIT in Marburg, SPHIC in
Shanghai and with a modified RFQ and intertank section
ITS for Medaustron, Wiener Neustadt. These 21 MV injectors run reliably since many years. Recently, higher pulsed
beam injector currents are requested in new efforts to makethe therapy treatment faster and/or more efficient.
To reach a compact and efficient linac design 25 years
ago, the layout was optimized for an 8 A keV beam fromthe LEBT with a normalized rms emittance of0.125 mm mrad. However, less than half the beam current
delivered by the all-permanent magnetic ECR-source Supernanogun [2] fits into that phase space at the RFQ injection point. At the HIT facility the beam losses are locatedat the RFQ and ITS, which consists of a quadrupole doublet
and xy- steerer only. The injector linac at present delivers
45 to 50 μA C .
With the RFQ redesign a significantly higher transmission along the RFQ and an improved matching into the ITS
are intended – resulting in a factor two of beam current improvement at the injector exit. Full transmission of thebeam as delivered by the LEBT will not be possible due tomeasured norm. 90% rms beam emittances of around
0.3 mm mrad.

____________________________________________†

U.Ratzinger@iap.uni-frankfurt.de

TUPB: Tuesday Poster Session
MC3.1 Industrial and medical accelerators

Figure 1: View on the new RFQ design and the existing
ITS (quadrupole doublet and steerer) at the right side.
The beam dynamics simulations were performed with
RFQGen [3] and used a compact layout along the bunchformation [4, 5]. The simulation of the end gaps including
the longitudinal field components [6] were managed bytracking the particles with TraceWin [7] through the electric fields as calculated by CST-Studio-Suite [8]. As thelongitudinal end-gap voltages are in the order of magnitudeof the vane-voltage one has to minimize the transit-timefactor of the entrance gap close to zero to avoid strong influence on the bunch-forming process along the RFQ. Thatmeans, that the effective gap length has to be an integer
multiple n of 𝛽 𝜆 = 5.73 mm. The choice was 𝑛 = 2. The
radial matcher consists of 4 cells. The length between the
TUPB023
371

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A NEW RFQ FOR THE CARBON THERAPY INJECTORAT HIT HEIDELBERG

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB025

PHASE SETTING ISSUES FOR THE SPIRAL2 LINAC

Abstract
The SPIRAL2 superconducting LINAC accelerates
beams of different species, in a large energy range. During
operation, the beam requested by the physics can changequite often and it is mandatory that beams that have alreadybeen tuned can be obtained again by simple application of
the machine parameters already used. This reduces the accelerator retuning time and increases the machine availability for the physics experiences.
Voltages and more particularly phases of all the cavities
are among the crucial parameters for a quick retuning.
Proper beam tuning is monitored via the BPM (Beam Position Monitor) system.
This paper focuses on the RF and beam phase issues, reminds the way the reference frequency distribution, the
LLRF and the BPM work and are used in the tuning procedures, and summarizes the upgrade foreseen to improve thephase setting and monitoring reliability.

INTRODUCTION
The accelerator is presently operated with only one experimental hall: NFS (Neutron For Science), which mainly
requires protons and deuterons beams. Nevertheless, a second one: S3 (Separated Superconducting Spectrometer),dedicated to heavy ion physics is under commissioning,
and a second injector (NEWGAIN project) is being constructed to extend the ion variety as shown in the last column of Table 1.
During operation, the beams may vary depending on theuser requirements. Particle changes occur 4 to 6 times per

run under current conditions, and will increase in the coming years. For a quick retuning, it is mandatory to ensurethat previously tuned beams are reproducible through thesimple application of the machine parameters already used,among which voltages and more particularly phases of all
the cavities. Cavity phase setting stability depends on thereliability of the reference frequency distribution and of the
LLRF.
Table 1: Spiral2 Beams
Particles
A/Q
Max Current [mA]
Max Energy [MeV/A]
Max Beam Power [kW]

H+
1
5
33
165

D+
2
5
20
200

IONS
3
7
1 0.3414
7
44 17

REF. FREQUENCY DISTRIBUTION
The SPIRAL2 accelerator works at a single frequency of
88.0525 MHz and the master oscillator (MO) is a commercial synthesiser, with stability around 10-6.
This MO signal is amplified to drive a transmission line
(TL) containing several directional couplers and ended ona matching load as shown in Fig. 1. The amplifier is a 1 kW
unit, expected to be used at ~710 W (58,5 dBm) for operation margins, whose output power is stabilized within better that 1%. The TL is a 7/8” one (rated for ~7 kW), runningaside à water-cooled rubber pipe whose temperature is stabilized at 26°±2 °C, and is almost 40 meters long. A thermal case envelopes the TL and the pipe, from the first to

Figure 1: Schematics of the reference frequency distribution for LLRF and diagnostics.

TUPB: Tuesday Poster Session
MC4.4 Low level RF

TUPB025
375

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M. Di Giacomo †, J-F. Leyge, Ch. Jamet, A. Orduz, P. Salou, GANIL, Caen, France

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB026

C. Kleffner, A. Schnase, A. Seibel, C. Muehle, C. Will, G. Schreiber, K. Knie, M. Rodionova,
M. Vossberg, M. Schuett, P. Forck, R. Hettinger, S. Udrea, S. Puetz, T. Sieber, V. Srinivasan
GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
H. Hähnel, U. Ratzinger, Goethe Universität Frankfurt, Frankfurt, Germany
Abstract
The progress and status of the high intensity short pulse
325 MHz proton linac driver for the FAIR facility in Darmstadt is described. The proton linac is designed to deliver abeam current of 70 mA at an energy of 68 MeV. The designof the normal conductiong CCH cavities was carried out incollaboration with our partners at the IAP Frankfurt and industrial partners. First bead pull measurements have beensuccessfully performed on the CCH prototype. This prototype cavity is intended for later final production and copper
plating. The construction of the ladder RFQ has been completed together with first rf measurements at levels up to
400 W. The RFQ has been delivered to FAIR and highpower rf tests are expected to be performed on site during
the next year. The proton driver, along with the antiproton
chain of the FAIR project, has been postponed due to a reprioritisation of the FAIR project and is now in a frozen
state. All delivered components need to be brought to astate that is consistent with the project objectives. This willallow a smooth re-launch in the future. The status of thisprocess is described in this paper.

CH-DTL
It is planned to complete the first of the series of CCH
coupled cavities, the CCH1, and put it into operation withRF [3]. The CCH1 cavity was manufactured by PINK anddelivered to GSI last year in a version with clamped drift
tube connectors. Low level RF bead pull measurements
were performed on site to verify the basic RF characteristics of the cavity. Final electroplating tests on a dummy will
be carried out next year as a prerequisite for final production of the CCH1. At GSI the CCH1 cavity was set up on
the RF testbench (Fig. 2) to be able to performe bead pullmeasurements. The cavity was supplied with a complete
set of movable tuners for all 17 possible tuner locations. In
total, measurements were carried out with more than 120
different tuner positions (Fig. 3).

OVERVIEW
The main characteristics and structure of the proton linac[1, 2] are shown in Fig. 1 and Table 1. It consists of a 2.45
GHz ECR source generating 100 mA of 95 keV protons
followed by a low-energy beam transport line (LEBT), a
4-Rod ladder RFQ and six normal conducting crossbar
cavities of CCH and CH type arranged in two sections. The
design provides for the proton beam to go directly to theproton beam dump or with two 45° dipoles to the injection
beam line in front of the SIS18 synchrotron.
Table 1: Proton Linac Main Parameters
Particle

Proton (H+)

Ion source
MEBT energy
CCH section
Final energy
Pulse current
RF-frequency
Rep. rate

95 keV
3 MeV
33 MeV
68 MeV
70 mA
325.224 MHz
2,7 HzFigure 2: CCH1 cavity in preparation for bead pullmeasurements (1). Photo of the first CCH1 section (2).
Photo tele shot along all drift tubes of the cavity (3).

Figure 1: Layout of the FAIR Proton Linac.
TUPB: Tuesday Poster Session
MC3.4 Proton linac projects

TUPB026
379

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PROGRESS AND STATUS OF THE FAIR PROTON LINAC

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB027

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HIGH CURRENT MACHINE CAMPAIGN
WITH VARIOUS ION SPECIES AT GSI UNILAC
H. Vormann1,∗ , W. Barth1,2,3 , F. Dziuba1,2 , S. Lauber1,2 , J. List1,2 ,M. Miski-Oglu1,2 , U. Scheeler1 , M. Vossberg1 , S. Yaramyshev1
1 GSI Helmholtz Centre for Heavy Ion Research, Darmstadt, Germany
2 HIM Helmholtz Institute Mainz, Mainz, Germany
3 KPH Johannes Gutenberg Universtity Mainz, Mainz, Germany
Abstract
After dedicated machine upgrade measures at the GSIUNILAC (UNIversal Linear ACcelerator), a high current
beam campaign has been performed recently. The presented
results were successfully accomplished, including newly installed electrodes for the superlens (short RFQ-type matching section). Beam experiments have been conducted withhigh intensity proton beam (1.2 mA), carbon (1 mA 12 C6+ )and nitrogen beam (6.5 mA 14 N7+ ) dedicated for pion production. A record argon beam intensity of 28 mA (40 Ar11+ )has been obtained at gas stripper section. A sufficiently highstripping efficiency of 35% applying a pulsed N2 gas stripper
target could be realized. By achieving high-current performance for medium-heavy ions, a further step has been taken
towards fulfilling the FAIR requirements for space charge
dominated operation. In this contribution the results of machine experiments are summarized, in particular the performance enhancement at the High Current Injector (HSI).

INTRODUCTIONThe UNILAC is utilized for all ions of different masses
from protons to uranium. It consists of different ion source
terminals, the High Current Injector HSI with the adjacentstripping section, the poststripper, a chain of ten single gap
resonators and the transfer channel to SIS18 (Fig. 1, [1–6]).

ION BEAM INVESTIGATIONSIn November and December 2023 measurement campaigns have been conducted with high intensity light andmedium ion beams (protons, carbon, nitrogen, argon).
HSI-superlens-operation suffered from performance restrictions until 2022. Therefore, since 2023 high intensity
heavy ion beam operation is again possible and has evenbeen significantly improved.

HSI RFQ and Superlens Optimization
The HSI-RFQ RF performance was significantly degradated in 2017/2018, due to damages of the electrodes’ copper
surface from a long period of being held under atmosphereconditions, during repair measures in the one year shutdown
2017. After the replacement of its electrodes in 2019, the
RFQ is again able to accelerate all ion species, up to mass
to charge ratio of 62 [5].
The HSI superlens also showed degradation effects. As
a consequence the superlens rods have been exchanged in
2023, requiring additional RF-retuning, applying a modified
RF plunger design. Collimation of the horizontal beam size
were introduced to avoid beam loss inside the superlens
cavity. The superlens upgrade resulted a in full performancerecovery.

Proton and Carbon Beam Investigations

Figure 1: Overview of the GSI UNIversal Linear ACcelerator (UNILAC).
In the HSI ion beams are accelerated from 2.2 keV/u to
1.4 MeV/u with an RFQ and two IH-DTL-tanks. The poststripper contains five Alvarez type DTL-tanks and a chainof ten single gap resonator cavities. The nominal output
beam energy is 11.4 MeV/u. Lower energies can be chosen
by individually turning off Alvarez cavities, fine tuning isaccomplished with the single gap resonator chain.
∗ h.vormann@gsi.de

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382

Proton beam generated by stripping the CH3 beam (MUCIS) from HSI was accelerated to the maximum lintensity
at UNILAC and SIS18 and maximum energy of 4.7 GeV/u.
From 1 mA 15 CH3 1+ at 1.4 MeV/u, a proton beam intensityof up to 1.2 mA at the end of the transfer channel could bereached (70% of UNILAC design limit). Intensity optimization suffered from an exceptional unstable beam position,
due to insufficient stability of the power supply of a dipole
magnet. Higher proton beam intensity is possible, if operation of the DTL tanks at a nominal synchronous phase of–30° would be applied. Nevertheless, an intensity of up to
1·1011 particles on SIS flattop could be achieved.
Proton beam operation was conducted with dedicated Alvarez RF phase settings, as already used in regular operation
since 2021: The synchronous phase is shifted from –30°
(regular for heavy ions) to –57°, so a reasonable (not toolow) RF power can be applied, leading to poststripper operTUPB: Tuesday Poster Session
MC3.3 Other proton/ion

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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UPDATE ON THE INTENSE HEAVY ION DTL PROJECTALVAREZ 2.0 AT GSI
L. Groening∗ , T. Dettinger, M. Heilmann, M. S. Kaiser, S. Mickat
GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany
Abstract
The Alvarez-type post-stripper DTL at GSI accelerates
intense ion beams with A/q≤8.5 from 1.4 to 11.4 MeV/u.
After more than 45 years of operation, it suffers from aging and its design does not meet the requirements of theupcoming FAIR project. Prototyping of a new 108 MHz
Alvarez-type DTL has been completed and series components for the 55 m long DTL are under production and havebeen delivered partially. This report summarizes the actual
status of Alvarez 2.0 at GSI and sketches the future path tocompletion.

INTRODUCTION

shall be served as well. The DTL design allows for switching
off the RF-power of the last cavities while the transversely
focusing quadrupoles inside the drift tubes remain switchedon. Accordingly, the DTL output energies correspond to
the individual cavity exit energies of 3.212, 5.173, 7.142,
9.237, and 11.318 MeV/u. The quadrupoles are pulsed,
such that focusing can be adapted individually to each ion
species and design energy; the latter can be changed between
the individual DTL pulses, i.e., within less than 100 ms.
The DTL design is described in detail within the dedicatedTechnical Design Report [3] and the main design parameters
are listed in Table 1.

Like the current DTL, the new section will accelerateions up to the injection energy of the subsequent synchrotron SIS18. All species up to the mass-to-charge ratioof A/q=8.5 are accelerated, corresponding to FAIR’s reference ion of 238 U28+ [1]. Five cavities with lengths of about
11 m each are operated at 108.4 MHz with peak powers of
up to 1.35 MW including beam loading. Figure 1 plots the
new DTL together with some RF-design details of the firstcavity. The normal conducting DTL covers a beam repetition rate of up to 10 Hz with flat top RF-pulse length of up
to 1.0 ms corresponding to the beam pulse length. Within

Table 1: Main Design Parameters of GSI’s New PostStripper DTL Alvarez 2.0 [3]Figure 1: New post-stripper DTL Alvarez 2.0 under construction at GSI.

PRODUCTION OF CAVITIES

the cavities, transverse FDDF focusing is provided with azero current phase advance of 65o . The large intensities
cause transverse tune depressions of up to 40% along thefirst cavity [2]. Longitudinal focusing is from RF-phases of−30o along the first three cavities and −25o along the last
two ones. Cavities are separated by four identical inter-tank
sections [2] which serve for 3D beam envelope matchingby three quadrupoles and one re-buncher. The inter-tank
sections provide also for a beam current and phase probe,a sector valve, and a transverse beam profile measurement
set-up.
Although the machine is mainly designed as an injector
for the synchrotron SIS18, several low-energy experiments∗ la.groening@gsi.de

TUPB028386

Parameter
Ion A/q
Input beam energy
Output beam energy
Electrical beam current
Transv. tune depression
Beam pulse duration
Beam repetition rate
Number of cavities
RF-frequency
Max. RF-power per cavity
RF-sources per cavity
Transv. focusing scheme
Total length

Value≤ 8.5 (238 U28+ )1.358 MeV/u
3.212 −11.318 MeV/u
1.76 emA⋅ A/q≤ 40 %
0.2 −1.0 ms≤ 10 Hz5
108.408 MHz
1.35 MW
1
FDDF
55 m

Each of the five cavities comprises five cavity sections
from stainless steel. The mantle has a strength of 12 mm.
Its roundness with a tolerance of the average radius of−0/+0.3 mm has been achieved by rolling without millingas well as the tolerance in length of ±0.1 mm. The mantle
is equipped with external cooling channels. Of special concern is the high quality of the inner surfaces for subsequent
bright Cu-plating. The surface must be free of voids andits roughness 𝑅𝑎 must not exceed 0.3 µm. Production has
been started in summer 2022 at one single manufacturer(see Fig. 2), after successful testing of a fully RF-operated
FoS cavity section [4]. Effective duration of production isabout seven weeks per section, including also the 5×2 cavity end plates. The sections of the first cavity have beendelivered in spring 2024 and those of the second cavity in
TUPB: Tuesday Poster Session
MC3.2 Ion linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB029

CONSIDERATIONS AND FINDINGS ON BEAM VORTICITY DYNAMICS

Abstract
Rotation of beams is usually quantified through angularmomentum rather than through vorticity. However, the difference of the two transverse eigen-emittances is linked morestrongly to vorticity than to angular momentum. It has beenfound that the dynamics of vorticity has remarkable similarity to the dynamics of the beam envelope along channelsof solenoids and quadrupole triplets. Transport matrices ofvorticity, corresponding phase advances, and Twiss parameters look very similar and are partially even identical to theircounterparts concerning envelopes. Corresponding to emittance, the quantity of vortissance, being a constant of motion,
is defined. Unlike emittance, for vorticity-dominated beams,
it may take imaginary values causing imaginary Twiss parameters and negative or zero phase advances along a finite
beam line section.

ANGULAR MOMENTUM AND VORTICITY
The rms angular momentum of a particle beam is defined
through the beam’s second moments as
𝐿 := ⟨𝑥𝑦 ′ ⟩ − ⟨𝑥 ′ 𝑦⟩ .

(1)

Usually, the angular momentum is regarded as the quantification of rotation being justified by its outstanding role inphysics. Nevertheless, other quantities may serve for thispurpose as well, among them for instance the beam vorticity∫ hi® × 𝑟® ′ · 𝑑 𝐴® ,
V = 𝐴
∇
(2)

Figure 1: Ellipse with aspect ratio 𝑟 performing a rigid
rotation (upper) and an intrinsic rotation (lower).

(V/𝐴)𝑖𝑛𝑡 =𝜔 2
𝑎 (1 + 𝑟 2 ) .
4(8)

The above expression for vorticity may be re-phrased [1] as

The expressions for 𝐿 and V/𝐴 flip when flipping from rigid
to intrinsic rotation. Additionally, for extreme aspect ratiosof 𝑟 ≪ 1 or 𝑟 ≫ 1, the rigid rotation has just angular momentum and vanishing 𝑉/𝐴 (relatively), while the intrinsic
rotation has just 𝑉/𝐴 but vanishing angular momentum (relatively). Another special case is the circle (𝑟 = 1) and justfor objects with cylindrical symmetry, angular momentum
is equal to vorticity

V = ⟨𝑦 2 ⟩⟨𝑥𝑦 ′ ⟩ − ⟨𝑥 2 ⟩⟨𝑦𝑥 ′ ⟩ + ⟨𝑥𝑦⟩(⟨𝑥𝑥 ′ ⟩ − ⟨𝑦𝑦 ′ ⟩) . (4)

𝐿 = V/𝐴 .

Figure 1 illustrates the difference between angular momentum and vorticity using an ellipse performing two types ofrotation.
Determining the angular momentum and V/𝐴 reveals forthe rigid rotation [1]Vorticity enters into beam dynamics through its tight relation to the two transverse eigen-emittances 𝜀 1 and 𝜀 2 [2]of a beam. The latter are equal to the two projected rms
emittances, if and only if all correlations between the twotransverse planes have been removed to zero. Removing
them preserves the eigen-emittances and changes the projected emittances.
Transverse beam eigen-emittances are calculated throughbeam rms moments as√︃√︁1
𝜀 1/2 =
−𝑡𝑟 [(𝐶𝐽) 2 ] ± 𝑡𝑟 2 [(𝐶𝐽) 2 ] − 16 𝑑𝑒𝑡 (𝐶) ,
2
(10)
with

𝐴

obtained from the rotation of the derivative of the particle
beam position and the beam rms area
𝐴2 := ⟨𝑥 2 ⟩⟨𝑦 2 ⟩ − ⟨𝑥𝑦⟩ 2 .

𝜔 2
𝑎 (1 + 𝑟 2 ) ,4𝜔(V/𝐴)𝑟𝑖𝑔 = 𝑎 2 𝑟 ,2while for the intrinsic rotation one obtains
𝜔𝐿 𝑖𝑛𝑡 = 𝑎 2 𝑟 ,2𝐿 𝑟𝑖𝑔 =∗ la.groening@gsi.de

TUPB: Tuesday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

(3)

(5)
(6)

(7)

(9)

TUPB029
389

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L. Groening∗ , GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB030

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HIGH PERFORMANCE MEGAWATT URANIUM BEAMS AT GSI UNILAC
W. Barth1,2,3,†, F. Dziuba1,2, S. Lauber1,2, J. List1,2, M. Miski-Oglu1,2, U. Scheeler1, H. Vormann1,
M. Vossberg1, S. Yaramyshev1,2
1
GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany
2
Helmholtz Institute Mainz, Germany
3
Johannes Gutenberg-Universität Mainz, Mainz, Germany
Abstract
The 50 years operating GSI-UNILAC (Universal Linear
Accelerator) as well as the heavy ion synchrotron SIS18
will serve as a high current short pulse heavy ion injector
for the FAIR (Facility for Antiproton and Ion Research)
synchrotron SIS100. This contribution presents the resultsof the full performance high current uranium beammachine experiment campaign at UNILAC, conducted in
the last three years. In order to determine the behaviour of
uranium beams, the transverse beam emittance at five
selected measurement positions along the complete
UNILAC have been measured for the first time in several
machine investigation runs. A significant improvement inbeam brilliance was achieved after several upgrade
measures at the High Current Injector (HSI) by using thepulsed hydrogen stripper at 1.4 MeV/u. It could be shownthat extremely low horizontal emittances, i.e. very highbrilliances, are achieved along the complete UNILAC up
to the SIS18 injection. Besides high intense uranium beams
with charge state 28+ also 1.5 Megawatt-multi charge
beams, comprising 27+, 28+, 29+ uranium ions, commonly
recharged primarily to charge state 73+ using a carbon foil,
were investigated and a record uranium beam current of
3.6 emA has been achieved.

INTRODUCTION
Besides the High Charge State Injector (HLI)
accelerating highly charged ions from an ECR ion sourceof CAPRICE-type, the High Current Injector (HSI), fed by
two ion source terminals and a low energy beam transportsystem (LEBT), serve as injector linac for the GSIUNILAC (Fig. 1). The HSI comprises a 36 MHz IH-RFQ(2.2 keV/u up to 120 keV/u) and an IH-DTL with two
separate tanks, accelerating the beam up to the final HSIenergy of 1.4 MeV/u. After stripping and charge state
separation the Alvarez DTL provides for beam acceleration
up to 11.4 MeV/u. In the transfer line (TK) to thesynchrotron SIS18 a foil stripper and another charge state
separator system can be used. In order to provide thehighest heavy ion beam currents (15 emA, U28+), as
required for FAIR, the HSI must deliver up to 2.8⋅1012 U4+ions per pulse [1-2]. With the AC beam transformers
installed behind each accelerator cavity and along alltransport sections, the beam transmission in all sections canbe permanently monitored and measured with highprecision. The positions of the emittance meters, used forthe measurements presented in this paper, are shown in
Fig.1.
___________________________________________† email address: w.barth@gsi.de
TUPB030
392

Figure 1: GSI-UNIversal Linear ACcelerator; emittancemeters at LEBT (1), gas stripper section (2), poststripper(3), transfer line (4 and 5) are shown in blue marks.

UNILAC-UPGRADE MEASURESFor the recent uranium beam campaigns at UNILAC, anovel multi-hole extraction system for extracting a highbrilliant ion beam from the VARIS ion source [3-4] wasused. Moreover, the HSI RFQ has been equipped with newmini-vane electrodes so that it could be again operated atnominal RF-voltage for uranium operation by applying a
dedicated conditioning and development program. The
HSI-superlens also recently underwent an extensive
upgrade programme. The electrodes were also replaced, sothat uranium levels could be applied again without any
problems. To prevent beam losses in the tank, theelectrodes were protected by a suitable aperture
diaphragm.
During preparation stage of the superlens upgrade, thebeam emittances before and behind HSI-RFQ for highcurrent argon-beam have been measured again after morethan 12 years; the measured beam emittances are about
50% lower compared to the long past campaign. By
measuring the RF-voltage influence on the beamemittance, it was possible to show that the RFQ-working
point corresponds to minimum transversal emittance
growth (see Fig. 2). Backtracking of measured beamemittance to RFQ-exit and subsequent forward tracking
resulted in optimized superlens matching. A minimum
beam spot at superlens entrance was confirmed by a profile
measurement. Due to field strength limitations of theintermediate quadrupole duplet in front of the superlens,
the optimum uranium beam matching (avoiding further
beam losses) could be accomplished only by a newquadrupole duplet with increased field gradients.
The upgrade measures facilitated an extensive machine
optimizing program and thus the success of thismeasurement campaign. The already used pulsed hydrogen
stripping target [5] has been further optimized to enable forincreased gas densities [6], as well as to determine themaximum achievable average charge state. It was found,
TUPB: Tuesday Poster Session
MC3.2 Ion linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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MODELING BEAM DYNAMICS IN THE HELIAC ADVANCEDDEMONSTRATOR
S. Lauber ∗ 1,2 W. Barth1,2,3 , C. Burandt1,2 , F. Dziuba1,2,3 , R. Kalleicher2,3 ,T. Kürzeder1,2 , J. List1,2,3 , M. Miski-Oglu1,2 , U. Scheeler1 , H. Vormann1 , S. Yaramyshev1,2
1
GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
2
HIM Helmholtz Institute Mainz, Mainz, Germany
3
KPH Johannes Gutenberg-University Mainz, Mainz, Germany
Abstract
A crucial milestone towards the final expansion stage ofthe HELIAC (HElmholtz LInear ACcelerator at GSI Darmstadt) is the commissioning of the first fully equipped cryo
module, the so-called Advanced Demonstrator. The cryo
module comprises three superconducting crossbar H-mode
accelerating cavities, a rebuncher and two superconducting
solenoids. For modelling the beam dynamics of the Advanced Demonstrator test setup, the actual 3D electromagnetic field distributions of the cavities and solenoids are used.
The digital model was linked to beam-based measurementsof the longitudinal and transverse beam density distribution to realistically calculate the beam propagation alongthe 20 m long setup. The beam dynamics findings gained
during the cryo module commissioning are presented.

INTRODUCTION
The first cryo module (CM1) of the Helmholtz Linear
Accelerator (HELIAC) [1, 2] was subject to the first full integration test in the end of 2023. The cryo module is equippedwith four superconducting crossbar H-mode (CH) cavities[3–5] and two superconducting magnets for beam acceleration and focusing. An Ar8+ and He2+ ion beam (deliveredby the GSI HLI) was utilized to investigate the beam acceleration capabilities of the cryo module unit. Finally, the cryo
module provided beam energies up to 3.1 MeV/u with He2+ ,exceeding the foreseen 2.7 MeV/u design energy.
The cryo module has a minimal selection of beam diagnostics. Only cold beam position monitors are generally available, but have not been operated in the forementioned beamtime. For a better understanding of the employed
beam dynamics concept of the superconducting CH cavities(namely EQUidistant mUltigap Structure (EQUUS) [2, 6,7]) in practice, further knowledge about the beam transport
within the cryo module is desired. Through the use of adigital twin of the accelerator and a beam representation
based on measurements, it is possible to visualize the beam
dynamics as it passes the accelerator. This allows a more precise understanding of the accelerator performance in termsof transmission and beam quality.

METHODThe beamline has been modelled using the in-house developed beam dynamics solver Aperture3D [8] based on∗ s.lauber@gsi.de

TUPB031
396

Python. The software can be utilized with the highest flexibility to fit in the dynamic readout of the control system.
The application is able to display specific plots, it is intended
to be extended continuously.

Aperture3D
Aperture3D is a multi-particle code designed to describe
beam dynamics in linear accelerators. It calculates the propagation of charged particles through 3D electromagnetic
fields. The propagation is calculated in two steps. In thefirst step, the space charge forces acting on each particle(and other external forces if required) are calculated. All
these external forces are intended to have a relatively longevaluation time. After calculation of the external forces, theparticles are integrated through the electromagnetic fields
by using the Runge–Kutta 4 method, considering the 3D
electromagnetic fields 𝐸(𝑥, 𝑦, 𝑧, 𝑡) and 𝐵(𝑥, 𝑦, 𝑧, 𝑡) and the(for the second step temporarily static) external forces, until
the beam propagated several RF-periods. After this distance,
the beam shape has changed sufficiently in order to justify
updating and recalculating all external forces, avoiding manifold updates per RF period. The Python package Numba
is employed to balance the benefits of Python and the highperformance capabilities of compiled languages. Thus, thehigh computational workload can be managed by utilizing
CPU-parallel execution.

Beamline Model
A beamline model for the existing beamline has been
built using Aperture3D, incorporating the HLI partially andthe HELIAC cryo module CM1 (see Fig. 1). The beamline
description and modelling starts at the exit of the HLI IH
cavity at a beam energy of 1.4 MeV/u due to the availabilityof sufficient beam diagnostics. This allows both, the longitudinal and the transverse characterization of the beam. At
positions in the injector with lower energies, the longitudinal
reconstruction of the beam density is not feasible due to thelack of required instrumentation. Also, the prediction of thebeam dynamics inside the RFQ and IH are very demanding
and should be established extremely careful. As the main
scope of this investigation is the beam dynamics inside thecryo module, the calculations inside and before the IH are
not required.
For the modelling of the beamline, the position of all
beamline magnets, quadrupoles, solenoids, steerers and normal and superconducting cavities must be considered. FurTUPB: Tuesday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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PHOTOCATHODE STUDY IN SRF GUN-II AT HZDR
R. Xiang†, A. Arnold, S. Gatzmaga, G. Hallilingaiah, A. Hoffmann, P. Murcek, R. Niemczyk,
A. Ryzhov, J. Teichert, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
Abstract
HZDR’s SRF Gun-II is an excellent demonstration of
SRF technology application in the field of electron sources
operating in continuous wave mode. As well known, quality of the photocathode is crucial for operational stability
and reliability of an SRF gun. In this contribution, various
studies on Cs2Te cathodes, including cleaning, preparation,transport/insertion, RF and beam operation will be summarised. We will look back at the achievements and open issues, and discuss possible improvements and further development.

INTRODUCTION
Development of high-quality electron photo-sources is a
key research field in particle accelerator technologies,
which is crucial for both fundamental and applied research.
It is widely acknowledged that quality of photocathodes
plays an essential role in enhancing the stability and reliability of photo-injectors [1]. A “perfect” photocathodeshould provide a high quantum efficiency (QE) at a standard laser wavelength, long lifetime, fast response and low
thermal emittance.
For the development of SRF guns at HZDR, metal cathodes (copper, magnesium) and a type of semiconductor
photocathodes, Cs2Te, have been selected. During lastyears, with Cs2Te photocathodes the SRF Gun-II has beenable to provide stable beams for accelerator users [2].

work function of Cu (4.6 eV) is relatively high, and its
quantum efficiency (QE) of 1×10-5 at 260 nm is insufficient for routine beam production. In the context of medium bunch charge mode, a magnesium cathode is a promising candidate. Magnesium is a metal with a low work
function of 3.6 eV, while its QE can reach 0.5% after ps
UV laser cleaning [3]. Despite its lower QE compared to
Cs2Te, Mg offers the benefits of a longer operational lifetime, reliable compatibility, and minimal risk of contaminating the niobium cavity.
Since May 2020, Cs2Te photocathode (with a band gapof 3.3 eV and an electron affinity of 0.2 eV) has demonstrated favorable QE and a prolonged operational lifetimein the ELBE SRF gun-II [4]. Due to the overheating observed in the cathodes within the SRF gun cavity, the decision was taken to use high conductive copper (OFHC) instead of Mo plugs, despite the inherent challenges associated with utilising copper as a substrate for Cs2Te. Cs2Te
on Cu plugs have been prepared at HZDR and have demonstrated successful operation within SRF gun-II during theTHz user beam time as well as possibility of high average
current (up to 1 mA) operation.

HZDR SRF GUN-II AND CATHODESHZDR SRF gun-II was built for the super-radiant THz
source at ELBE SRF accelerator. Currently, the SRF gunII is providing more than 1000 hours beam time yearly for
ELBE.
The SRF gun-II includes a 3½ cell 1.3 GHz cavity withchock cell and a SC solenoid in a cryostat, and a load-locksystem for cathode exchange. It is operated with Cs2Te
cathodes driven by a 260 nm laser. The bunch charge is up
to 250 pC at the repetition rate of 50 kHz or up to 80 pC at
13 MHz. The kinetic energy is limited to 3.5 MeV by fieldemission in the SRF cavity.
A highlight of HZDR SRF gun-II is that the cavity gradient has not significantly degraded despite multiple cathode exchanges Even after overheated Cs2Te evaporated in
the gun in 2017, it was possible to recover the cavity.. This
well demonstrates possibility of routine operation of an
SRF gun.
By now, 31 cathodes have been in use in SRF gun-II,
including 2 bulk-Cu plugs, 3 Cs2Te on Mo plugs, 12 bulk
Mg cathodes, and 14 Cs2Te on Cu plugs (see Fig. 1). Copper was employed as the commissioning cathode. The

Figure 1: Cathodes used in SRF Gun-II.

CS2TE PREPARATION PROCESSThe Cs2Te photocathodes were prepared in the HZDR
cathode laboratory and transported to the SRF gun via a
vacuum transfer system. In the course of our experiments,
the Cs2Te cathodes on the mechanically polished plugs andthose on the diamond-turning finished plugs exhibitednearly identical photoemission quality and also the samedark current in the gun. The plugs were meticulously
cleaned in a cleanroom. To maintain the surface free of any
contamination, chemical cleaning, dry ice cleaning, and
350°C baking in a vacuum were employed.
During the preparation process, the plug was kept at
120°C by means of a halogen lamp. First, tellurium was____________________________________________†

r.xiang@hzdr.de

TUPB034
400

TUPB: Tuesday Poster Session
MC1.2 Electron and ion sources, guns, photo injectors, charge breeders

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISSN: 2226-0366

doi: 10.18429/JACoW-LINAC2024-TUPB035

DEVELOPMENT OF AN INTEGRATED MONITOR SYSTEMFOR REAL-TIME RELATIVE PHASE MEASUREMENTBETWEEN THE CAVITY-RF AND BEAM
E. Cicek∗ , Z. Fang, Y. Fukui, K. Futatsukawa, T. Miyao, S. Mizobata, KEK, Ibaraki, JapanJ. Kamiya, K. Moriya, S. Shinozaki, JAEA, Tokai, Naka, Ibaraki, Japan
Y. Sato, NAT Corporation, Tokai, Naka, Ibaraki, Japan
Abstract
In a linear accelerator, phase drift in upstream cavities canadversely affect downstream cavity synchronization, leading
to momentum drift and beam loss. J-PARC LINAC employs
different phase reference signals for beam monitoring and RF
systems, hindering direct comparison. Recent observations
revealed susceptibility of reference signals to environmental
effects in the Klystron Gallery. Hence, a thorough observation of the relative phase between cavity-RF and beam isimperative. Addressing this, we took advantage of the newly
developed MicroTCA.4-based monitor digitizers to meticulously analyze RF signals from cavity pick-up and beam
signals from existing fast current transformers dedicatedto measuring beam phase. Initial results show enhanced
long-term stability in the relative phase with a shared RF
reference. A beam study was also conducted wherein deliberate alterations were made to the cavity-RF phase settings
via the LLRF system to detect their impact on the phase driftof downstream cavities. The system recorded downstream
beam oscillations prompted by phase drift in upstream cavities. Our work elucidates a real-time monitoring strategy
for relative phase detection.

INTRODUCTION
The linear accelerator (LINAC) in Japan Proton Accelerator Research Complex (J-PARC) comprises a negativehydrogen (𝐻 − ) ion source (IS), a radio-frequency quadrupole(RFQ) linac, a drift-tube linac (DTL), a separated-type drifttube linac (SDTL), and an annular ring coupled structure(ACS). This configuration also includes a 50-keV low-energy
beam transport line (LEBT), a 3-MeV medium-energy beamtransport line (MEBT1) with two crucial buncher cavities(Buncher1 and Buncher2), and an RF chopper. The assembly extends through a 191-MeV medium-energy beam transport line (MEBT2) and culminates in the linac-to-3-GeV
synchrotron beam transport line (L3BT), as illustrated inFig. 1 [1,2]. The LINAC is equipped with various beam monitoring devices, including fast current transformers (FCTs)
dedicated to beam phase and energy measurements [3, 4].
In linear accelerators, phase drift in upstream cavities candisrupt synchronization in downstream cavities, resulting
in momentum drift and potential beam loss. The LINAC
uses different phase reference signals for beam monitoring
and RF systems, complicating direct comparisons. Specifically, the RF distribution system operates at frequencies of∗ ecicek@post.kek.jp

TUPB: Tuesday Poster Session
MC4.1 Beam diagnostics

312 MHz and 960 MHz [5], while beam monitor functions at
324 MHz. Recent observations have also highlighted the susceptibility of reference signals to environmental influencesin the Klystron Gallery. Consequently, a direct measurementof the relative phase between the cavity-RF and beam is
crucial.
To address this challenge, we utilized a micro telecommunications computing architecture (MicroTCA.4)-based
beam-monitor digitizer [6], a device within the monitoring
infrastructure developed for beam diagnostics purposes. The
board of the digitizer includes eight analog-to-digital converters (ADCs) operating at a maximum of 370 MSPS with
16-bit resolution and 800-MHz bandwidth, as well as twodigital-to-analog converters [7]. The DC-coupled ADCs
measure signals from FCTs and slow current transformers,
while 324-MHz RF signals from the beam position monitors
are acquired using AC-coupled ADCs. Our objective was toprecisely analyze RF signals from cavity pick-ups and beam
signals from existing FCTs. Our investigation started withlong-term measurements to monitoring long-term stability.
Furthermore, we conducted a beam study to evaluate theimpact of intentional modifications to the cavity-RF phasesettings at the RFQ, Buncher2, and SDTL01 locations, as
indicated by the dashed blocks in Fig. 1. This study aimed toassess the influence of these adjustments on the phase drift
in downstream cavities and investigate phase relationshipbetween cavity-RF and beam, thereby providing insights
into improving the LINAC.

LONG-TERM MEASUREMENTS
Phase detectors are utilized for beam phase measurementsin the LINAC [8]. In this study, a setup was established using
phase detectors, buffer amplifiers, and newly developed monitor digitizers to capture signals from multiple FCT monitorsand measure the long-term relative phase (see Fig. 2). The
324-MHz RF signal from a cavity is routed to the digitizer
through a phase detector, while 324-MHz signals from the
FCTs are routed through phase detectors and connected to thedigitizer via buffer amplifiers. A consistent 324-MHz monitor RF reference (REF#1∼REF#4, REFCLK) is distributed
to phase detectors and the digitizer and used to computecavity-RF and beam phases from each ADC channel.
The newly developed monitor digitizers, intentionallyplaced at various locations in the Klystron Gallery, facilitated a week-long measurement of the relative phase beTUPB035
403

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ISBN: 978-3-95450-219-6

JACoW Publishing32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB037

T. Miura†1, H. Katagiri, T. Kobayashi1, T. Matsumoto1, KEK, Tsukuba, Japan1
also at The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
Abstractlayout of the radio-frequency (RF) reference control anddistribution system [2]. The linac master oscillator (LMO)(Keysight E8663D) is 571.2 MHz, and the main ring master oscillator (RMO) is 508.9 MHz. The frequency ratio between LMO and RMO is 55:49, and the common frequency is 10.385 MHz. Both the LMO and RMO are generated by inputting 10 MHz, which is 510 MHz of the mainmaster oscillator (MMO) divided by 51, as the signal generator synchronization signal. For the SuperKEKB, a photocathode RF gun with a laser system was introduced to
produce the low-emittance electron beams for HER, and apositron damping ring (DR) was constructed in the middleof the linac for the low-emittance positron beams for the
LER. To accommodate these upgrades and ensure stablebeam injection into the rings, three new phase control systems are introduced for the RF reference in the injector.
The first is an MO phase feedback module (MOFB), introduced for drift compensation between the LMO and
RMO. If the phase drifts, the beam injection phase changes
and the injection efficiency worsens. The MOFB is required for stable injection and is placed immediately after
the LMO.
The second is an MO phase shifter (MOPS) for injection
phase control. The LMO phase must shift smoothly to theinjection phase for the HER or LER rings every 20 ms
which corresponds to a linac repetition rate of 50 Hz. However, the laser system of the photocathode RF gun does not
accept such rapid phase changes. Therefore, MOPS has
been developed to satisfy the requirements of the laser system and injection phase switching. The MOPS has two

The radio-frequency (RF) reference phase in the
SuperKEKB injector linac has been specially controlled forstable beam injection into the main rings (HER/LER). The
phase control system contains three parts: MOFB, MOPS,
and SECT35PS. MOFB is the phase feedback system fordrift compensation between the linac master oscillator(LMO) of 571.2 MHz and ring MO (RMO) of 508.9 MHz
which has a frequency ratio of 49/55 to the LMO. The
MOPS is an MO phase shifter for injection phase control.
The LMO phase must smoothly shift to the injection phasefor the HER or LER rings at a repetition rate of 50 Hz.
However, the laser system of a photocathode RF gun for
the HER beam does not accept such rapid phase changes.
Therefore, MOPS was developed to satisfy the requirements of the laser system and injection phase control.
SECT35PS is the phase shifter of the 2856 MHz RF reference downstream of the positron damping ring (DR) located in the middle of the linac. The DR is operated at thesame frequency as the main rings, 508.9 MHz. The linac
RF reference phase at the downstream of the DR is changed
from pulse to pulse by the bucket selection system to increase the synchronization probability for the bucket selection of LER ring. In this paper, we describe an RF reference
phase control system in the SuperKEKB injector linac.

INTRODUCTION
The KEK injector linac [1] is a facility that delivers low
emittance and high bunch-charge electron/positron beams
to the SuperKEKB HER/LER rings. Figure 1 illustrates theSuperKEKB Control Room

Linac Main Station

Linac MO

Main MO

Sync
10 MHz1/51

1/51

Sync MR MO
10MHz

509 MHz

510MHz571 MHzMR

DR MO

509 MHzMOFB

509 MHz

MOPS
10.385 MHz
114 MHz
2856MHz

Laser
SystemPLL

REF SG #1

EVG

2856MHz

114MHz571MHz

SB-A

SB-B

SB-C

Coaxial cable
Optical fiber (PSOF)

DR
Cont.RoomREF SG #2
LLRF cont units, RF monitors

RF-GUN

Sect35 PS

SB-5Phase-stabilized Optical Fiber Cable

O/E

E/O

SB-2

SB-1

SB-3

LLRF
Cont.Unit

SB-4

60kW
SB-klystron
I ΦA

T-Gun

To BCS

SHB

BCS

e+
TargetSSA

40MW
KlystronDR

SSA

To ECS

To e+ ECS

PF
AR

ECS

LER

RF-GUN

Sector A

Sector B

Sector C

Sector 1

Sector 2

Sector 3

Sector 4

Sector 5

HER

Figure 1: Layout of the RF reference control and distribution system at SuperKEKB injector linac.
___________________________________________† takako.miura@kek.jp

TUPB: Tuesday Poster Session
MC4.4 Low level RF

TUPB037
407

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RF REFERENCE PHASE CONTROL SYSTEM IN THE SuperKEKB
INJECTOR LINAC

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB038

T. Natsui†, KEK, Ibaraki, Japan
Abstract
The KEK injector linac injects electron and positron
beams into four rings: the high-energy ring (HER), lowenergy ring (LER), PF ring, and PF-AR. The HER and LER
are SuperKEKB main rings. The PF ring and PF-AR arelight source rings. These rings require several beams withdifferent charges and energies. The LER beam is a positron.
Simultaneous four-ring top-up injections were achieved in
50 pps. We have already installed pulsed magnets downstream of the linac for pulse-to-pulse difference beam injection. Pulsed quadrupole magnets require a pulsed current of 300 A. For these pulse magnets, we use an energyrecovery-type pulse driver. We can change the optics using
these pulsed quadrupole magnets and drivers.
However, the quadrupole magnet has a small aperture. It
cannot be installed in the upstream section because of its
large beam size; in particular, the positron primary electron
beam has the largest beam size. Thus, we installed a newlarger-aperture quadrupole magnet and high-power pulse
driver. The magnet current was 600 A, and the required
power was approximately four times higher than that of theold driver. In the summer of 2023, large-aperture quadrupole pulsed magnets were installed upstream of the linac.
The power of the new pulse driver was 600 A at 400 V,
which is an energy-recovery type. We achieved high efficiency with a simple pulse-width control. We intend to introduce this high-power and high-efficiency pulse driver.

INTRODUCTION
KEK has four storage rings for the electron/positron collider rings and two light source rings. The collider rings are
the high-energy ring (HER) and the low-energy ring (LER),
which are the SuperKEKB main rings [1]. The PF ring and
PF-AR are light source rings. Table 1 lists the injection
beam specifications for each ring. As the requirements ofthe beams were different, we changed the linac

acceleration conditions. We achieved simultaneous top-up
injection of the four rings using two types of electron guns
and several pulse magnets [2]. Figure 1 shows a schematicof the KEK electron/positron injector linac. We used a photocathode RF gun to generate the HER low-emittance electron beam. The required emittances were 40 and 20 mmmrad in the horizontal and vertical directions, respectively.
The other gun is a thermionic DC gun for the positron primary electron beam, which had a high charge of 10 nC perbunch. The DC gun is also used for the light source rings(PF and PF-AR). A positron beam is generated by hitting atungsten target in a flux concentrator (FC) with primaryelectrons [3]. A damping ring was used to reduce the emittance of the positron beam. The damping ring was installed
between Sectors 2 and 3, as shown in Fig. 1. In Sectors 3-5,
all the quadrupole magnets (Q magnets) are pulsed magnets. Downstream of the damping ring, the transverse beam
sizes were small in all modes; therefore, a pulsed Q magnet
with a 20 mm aperture could be used. This small-aperturetype magnet is called the PM_32_4 type. The Q magnets in
Sectors 3–5 were replaced by pulsed Q magnets in 2017[4]. The inductance of the Q magnet was 1.0 mH, and the
maximum pulse current was 330 A. The pulse driver raises
a current within 3 msec at a voltage of 220 V. However,these pulsed Q magnets and pulse drivers cannot be used
upstream of the injector because of the large positron primary beam size. In the bending sector (J-arc), we could not
independently match the beams because the Q magnets
were DC magnets.
Table 1: Specifications of Each Beam
Ring
HER
LER
PF ring
PF-AR

BeamElectronPositronElectronElectron

Energy7.0 GeV
4.0 GeV
2.5 GeV
6.5 or 5 GeVCharge4.0 nC
4.0 nC
0.3 nC
0.3 nCDC gunSector B

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DEVELOPMENT OF NEW PULSE DRIVER
FOR HIGH POWER PULSED MAGNET

Matching
Q magnets

Sector C

Sector A

FC
TargetRF gunDamping
Ring

LAS

Sector 1

Pulsed Q magnets

Sector 2

Sector 3

Sector 4

Sector 5

Figure 1: KEK injector linac consisting of eight acceleration sectors and a 180° bending sector. Sectors 3 to 5 have apulsed Q magnet. The new large-aperture quadrupole magnets were installed in the summer of 2023 for matching.
___________________________________________† takuya.natsui@kek.jp
TUPB038
410

TUPB: Tuesday Poster Session
MC2.2 Electron linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB039

Onur Gilanliogullari† , Pavel Snopok, Illinois Institute of Technology, Chicago, IL, USA
Brahim Mustapha, Argonne National Laboratory, Lemont, IL, USA
CIRCULAR MODE OPTICS

Abstract
Circular mode beams are beams with non-zero angularmomentum and strong inter-plane coupling. This coupling
can be achieved in linear accelerators (linacs) through magnetization of electrons or ions at the source. Depending on
the magnetization strength, the intrinsic eigenmode emittance ratio can be large, which produces intrinsic flatness.
This flatness can either be converted to real space flatness or
can be maintained as round coupled beam through the system. In this paper, we discuss rotation invariant designs thatallow circular modes to be transported through the latticewhile accelerating the beam and maintaining its circularity.
We demonstrate that with rotation invariant designs the circularity of the mode can be preserved as round beam while
maintaining intrinsic flatness to be converted to flat beam
for high brightness or injected into a ring.

INTRODUCTIONSpace charge effects at low energies are the limiting factor for achieving high-intensity high-quality beams. This
limit originates from two sources. Firstly, the current limit
due to extraction at the source. Secondly, the space charge
limit due to self Coulomb repulsion force and charge density
within the beam. Space charge forces are equivalent in thetransverse plane when the beam is round. When the beam
is flat, the quality parameters such as beam brightness andluminosity are enhanced due to small geometric beam sizein one dimension. At the same time, flat beams can not maintain high currents due to space charge effect, which tends toequilibrate the beam sizes. Circular modes are round beams
with intrinsic flatness and non-zero angular momentum as
discussed in Refs. [1, 2].
Since space charge forces depend on the beam distribution in space, circular modes behave in a similar fashion touncorrelated round beams while maintaining their intrinsic
flatness.
Magnetized beams can also be classified as circular modes,
where the beam experiences only one part of the solenoid’s
fringe field, which translates the canonical angular momentum to mechanical angular momentum. Extension of Bush’s
theorem discusses the angular momentum conversion fromthe magnetic field strength as discussed in Ref. [3].
In this paper, we will provide the background and define circular modes through coupling vectors. We will discuss formation of circular modes at the source and present
rotational-invariant linac lattice designs.
∗ This work was supported by the U.S. Department of Energy, under Con-

tract No. DE-AC02-06CH11357.

† ogilanli@hawk.iit.edu

TUPB: Tuesday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

Due to coupling, phase space vector parameterization
is expressed through coupled optics as shown in Ref. [4].
Phase space vector, 𝑧® = [𝑥, 𝑥 ′ , 𝑦, 𝑦 ′ ] 𝑇 , can be written as
𝑧® =

1√
1√
𝜖1 𝑣®1 𝑒 𝑖 𝜓1 +𝜖2 𝑣®2 𝑒 𝑖 𝜓2 + 𝑐.𝑐.,
2
2

(1)

where 𝜖1,2 are the eigenmode emittances, 𝜓1,2 the betatronphases, 𝑐.𝑐. stands for complex conjugate, and 𝑣®1,2 are theeigenvectors given by√√
𝛽1𝑥
𝛽2𝑥 𝑒 𝑖 𝜓2
© 𝑖 (1−𝑢)+𝛼1𝑥 ª©
ª√ 2𝑥 ®
­− √®
­ − 𝑖𝑢+𝛼­ √︁ 𝛽1𝑥 ®
­ √︁ 𝛽2𝑥 ®
𝑣®1 = ­ 𝛽 𝑒 𝑖𝜈1 ® ,𝑣®2 = ­
𝛽2𝑦 ®® . (2)
1𝑦
­
®
­
­
­ (1−𝑢)𝑖+𝛼2𝑦 ®
𝑖𝑢+𝛼1𝑦 ®
− √
−√
𝛽2𝑦
𝛽1𝑦
«
¬
«
¬
Here 𝛽1𝑥 , 𝛽1𝑦 , 𝛽2𝑥 , 𝛽2𝑦 are the coupled betatron functions,
𝛼1𝑥 , 𝛼1𝑦 , 𝛼2𝑥 , 𝛼2𝑦 the alpha functions, 𝑢 the strength of coupling and 𝜈1,2 the phases of coupling. As mentioned earlier,circular mode beams are intrinsically flat, 𝜖 2 ≪ 𝜖1 withflatness ratio defined as R = 𝜖1 /𝜖 2 . Due to intrinsic flatness,mode 2 contribution to phase space is small and the hasespace vector can be written as√︁√︁
𝑥 = 𝜖1 𝛽1𝑥 cos 𝜓1 , 𝑦 = 𝜖1 𝛽1𝑦 cos(𝜓1 − 𝜈1 ),√︂𝜖1′(−𝛼1𝑥 cos 𝜓1 − (1 − 𝑢) sin 𝜓1 )
𝑥 =
(3)
𝛽1𝑥
√︂
𝜖1
𝑦′ =
(−𝛼1𝑦 cos(𝜓1 − 𝜈1 ) − 𝑢 sin(𝜓1 − 𝜈1 )).
𝛽1𝑦
The phase of coupling determines the shapes of beam projections onto the different phase space planes. The projection
onto real space is given by
𝑥2
2𝛼˜
𝑦2
−
𝑥𝑦
+
= 1 − 𝛼˜ 2 ,2𝜎𝑥2 𝜎𝑥 𝜎𝑦
2𝜎𝑦2
√︁
√︁
𝜖 1 𝛽1𝑥 𝛽1𝑦 cos 𝜈1 + 𝜖 2 𝛽2𝑥 𝛽2𝑦 cos 𝜈2
𝛼˜ =
,
√︁
√
𝜖1 𝛽1𝑥 + 𝜖2 𝛽2𝑥 𝜖1 𝛽1𝑦 + 𝜖 2 𝛽2𝑦(4)where the beam distribution can be tilted in the (𝑥, 𝑦) space.
Disregarding mode 2 contribution will simplify the projection equation to
𝑦2
𝑥2
2𝑥𝑦
−
cos
𝜈
+
= sin2 𝜈1 .
1
2𝜎𝑥2 𝜎𝑥 𝜎𝑦
2𝜎𝑦2

(5)

In order to satisfy round beam condition, the phase of coupling needs to be π/2 and the optics functions, 𝛽1𝑥 = 𝛽1𝑦 =𝛽0 . Furthermore, based on circular mode properties, thestrength of coupling is determined to be 𝑢 = 1/2. This leads
to interesting relations, such as
TUPB039
413

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CIRCULAR MODES FOR LINACS∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB045

J. Yoon∗ , Y.-W. Jo, Y. Jung, Y.-K. Kim
Institute for Rare Isotope Science, Daejeon, Republic of Korea
D. Cha, D.-K. Lee, Vitzro Nextech Co., Ltd., Ansan, Republic of Korea
Abstract
A heavy-ion accelerator facility was constructed for theRare Isotope Science Project (RISP) at the Institute for Rare
Isotope Science (IRIS) in Daejeon, Korea. A cryomodulewith quarter-wave resonators (QWRs) and half-wave resonators (HWRs) was installed in the SCL (Superconducting
Linac) 3 tunnel, and the initial beam commissioning using argon beams has been completed. Additionally, a cryomodulewith single-spoke resonators (SSRs), power couplers, andtuners is currently under development for the SCL2 project.
The geometry of the fundamental power couplers (FPCs)
for the SSRs is a coaxial capacitive type based on a conventional 3-1/8 inch Electronic Industries Alliance (EIA) 50 Ω
coaxial transmission line with a single ceramic window. A
multi-physics analysis, incorporating electromagnetic, thermal, and mechanical aspects, was conducted to evaluate
the design of the power coupler for the SSRs. This paper
presents the results of the multi-physics analysis and thecurrent design status of the power coupler for the SSRs.

DESIGN UPDATE
To minimize the emission of electrons, the impedance had
to be increased, which consequently reduced the diameterof the antenna (vacuum section) compared to a conventional
3 18 -inch Electronic Industries Alliance (EIA) 50-Ω coaxial transmission line (TL). Figure 1 shows the difference
between the previous design and the updated design.

INTRODUCTION
SCL2 consists of two cavity types, SSR1 and SSR2, witha resonant frequency of 325 MHz. The difference between
SSR1 and SSR2 is the ratio of the particle’s velocity to the
speed of light, denoted as 𝛽 = 𝑣/𝑐, with values of 0.3 and
0.51, respectively. Additionally, the accelerating voltage
differs, being 2.35 MV for SSR1 and 4.2 MV for SSR2.
While the fundamental power coupler (FPC) for each cavity
type must have different design characteristics, the FPC
design for SSR1 and SSR2 can be the same due to theirresonant frequency of 325 MHz; the main differences of the
FPC are the required power and optimum external quality
factor. In this study, we present the updated design of the
FPC for 325 MHz SSRs at IRIS. The main parameters arelisted in Table 1.
Table 1: Main Parameters of the FPC
Parameter

Value

Operating frequency
Reflection coefficient (FPC only at 325 MHz)
Operating power (Nominal)
Operating power (SSPA)
Optimum external quality factor
Impedance of the vacuum section
Impedance of the air section

325 MHz< -20 dB
3 kW
7 kW
5.2 ×10690 Ω
50 Ω∗ foryjy12@ibs.re.kr

TUPB: Tuesday Poster Session
MC4.8 Superconducting RF

Figure 1: (top) Previous design and (bottom) updated design.
Since the dimensions of the inner conductor are the same
in both cases, the results of the electromagnetic field analysis are also identical. The outer conductors are plated with
10 µm of copper, approximately three times the skin depth(𝛿𝐶𝑢,325𝑀 𝐻 𝑧 = 3.62 µm). The T-box allows the supply of RF
power to the power coupler via a coaxial transmission line
and includes an inner conductor cooling line. The updated
design features bellow on the outer and inner conductors
within the cryomodule to protect the RF window from mechanical overload [1, 2].
This design allows for the addition of three pick-up ports
to monitor arc discharge, electronic emission, and vacuum
level variations, which helps prevent RF window breakage. To avoid dew point conditions on the RF window, two
Kapton film heaters (maximum 25 W) are attached to theouter conductor on the RF window section to maintain room
temperature.
TUPB045417

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

DESIGN UPDATE OF THE POWER COUPLERS FOR THE SINGLE-SPOKERESONATORS IN INSTITUTE FOR RARE ISOTOPE SCIENCE

.IOD dna ,rehsilbup ,krow eht fo eltit ,)s(rohtua eht ot noitubirtta niatniam tsum krow siht fo noitubirtsid ynA .)4202 ©( ecnecil 0.4 YB CC eht fo smret eht rednu desu eb yam krow siht morf tnetnoC

PRELIMINARY DESIGN OF TRANSVERSE DEFLECTING STRUCTURE
SYSTEMS FOR SHENZHEN SUPERCONDUCTING SOFT-X-RAY FREE
ELECTRON LASER
Z. Li†, J. Shao, Q. Huang, L. Wei, Institute of Advanced Science Facilities, Shenzhen, China
J. Yang, W. Zhang, Dalian Institute of Chemical Physics, CAS, Dalian, China
Abstract
Transverse Deflecting Structures (TDS) are commonlyused in Free Electron Laser (FEL) facilities for the measurement of longitudinal information of electron beam, including bunch length, temporal distribution, slice emittance, etc. Shenzhen Superconducting Soft-X-ray Free
Electron Laser (S3FEL) is a high-repetition-rate FEL recently proposed for scientific research and applications. In
S3FEL, TDSs that work at S-band (2997.222 MHz) and Xband (11988.889 MHz) will be utilized for the diagnosis
and analysis of longitudinal phase space of electron
bunches along the beamline. In this manuscript, we present
the preliminary design of both S-band and X-band TDS
systems of S3FEL, including system layout, deflecting
structures, pulse compressors, RF distribution networks,etc. Additionally, we introduce a new parallel-coupled TDS
cavity with variable polarization for multi-dimensional
phase space diagnostics.

Figure 2: Layout of S3FEL.
Table 1: Main Parameters of S3FELParameter
Beam Energy
ChargeRep. Rate
FEL Wavelength

Value
2.0~2.5100
1
1~30

TDS SYSTEMS OF S3FELIASF & S3FEL
Institute of Advanced Science Facilities, Shenzhen(IASF), founded in 2020, is a multi-disciplinary research
institute responsible for Shenzhen's large-scale science facilities' whole life cycle planning, construction, operation,and maintenance. The Institute is located in Guangming
District, which aims to be the science center of Shenzhen.
At this stage, two projects are being proposed: Shenzhen
Innovation Light-source Facility (SILF), and Shenzhen Superconducting Soft X-ray Free Electron Laser (S³FEL) as
shown in Fig. 1. Both are planning to be constructed in
ISBN: Guangming
978-3-95450-219-6 District, Shenzhen [1]. ISSN: 2226-0366

Unit
GeV
pC
MHz
nm

Transverse Deflecting Structures (TDS) are designed for
longitudinal and transverse phase-space diagnostics in
S³FEL. The RF frequencies of TDS systems are decided
according to bunch energy and bunch length. When bunchenergy ≤300 MeV, S-band TDSs will be applied with an
RF frequency of 2997.222 MHz. When bunch energy＞
300 MeV, X-band TDSs will be used with a frequency of
11988.889 MHz. Totally 5 S-band TDS units and 5 X-bandones are considered as listed in Table 2.

doi: 10.18429/JACoW-LINAC2024-TUPB048

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA

JACoW Publishing

Figure 3: TDS system.
TDSs are powered by klystron as shown in Fig. 3. EachTDS unit contains TDS, waveguide network, klystron,
modulator, HV power supply, etc.
Figure 1: Architectural rendering of S3FEL.
S³FEL was approved in May, 2023, aiming to generate
MHz-repetition-rate soft X-ray FEL using superconducting
acceleration technology [2] at rates up to 1MHz (Fig. 2 andTable 1).
___________________________________________† lizongbin@mail.iasf.ac.cn

X-band TDS
As mentioned above, the deflecting voltage of X-band
TDSs should be no less than 24 MeV (@1 GeV bunch energy) and 48 MeV (@2.5 GeV bunch energy). A conventional LOLA-type TDS [3] scheme is being considered fornow.
Limited by klystron technology and the budget, we take

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB050

Z. H. Liang1,2†, M. Xu1‡, J. Y. Wang1, C. L. Li1, Q. T. Huang3, T. Tan1, L. B. Liu1, P. A. Xiang3,
S. X. Zhang1, H. Guo1, P. R. Xiong1, Y. He1
1
Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China
2
University of Chinese Academy of Sciences, Beijing, China
3
Advanced Energy Science and Technology Guangdong Laboratory, Huizhou, China
Abstract
Nuclotron-based Ion Collider fAcility (NICA) is anaccelerator complex under construction in JINR, in which
superconducting linac-injector can accelerate protons up
to 20 MeV and light ions to 7.5 MeV/u. To achieve thisdesign target, a 325 MHz, beta = 0.21 niobium half-wave
resonator (HWR) called HWR1 was developed jointly by
IMP and JINR. This paper optimizes the electromagnetic
design of NICA cavity, designs the mechanical structure(including helium jacket) and gives the results of multiphysical studies. Simulation results show that Epk/Eacc =5.88, Bpk/Eacc = 9.96 mT/(MV/m). In addition, theniobium cavity has been fabricated and vertically tested,
the magnetic shield and helium jacket are in the processof electron beam welding, and the cryomodule will beassembled in the next 1~2 months.

INTRODUCTION
The NICA project in Russia is a major scientificinitiative focused on exploring the properties of dense
nuclear matter. Located at the Joint Institute for Nuclear
Research (JINR) in Dubna, NICA aims to recreate
conditions similar to those of the early universe bycolliding heavy ions at high energies. The facility consistsof a complex of accelerators, including a superconducting
synchrotron and two collider rings, designed to accelerateions and polarized protons. The primary goal of NICA isto study the phase transitions between hadronic matter andquark-gluon plasma, providing insights into thefundamental forces governing particle interactions.
Through its unique capabilities, NICA will play a criticalrole in advancing our understanding of strong interactions
and the structure of matter under extreme conditions [1-4].
The existing linear injector LU20 has been in operationfor 50 years and is now considered outdated. As a result,the superconducting linear accelerator LILac has beendeveloped as a new injector [5-6]. The Institute of Modern
Physics, Chinese Academy of Sciences (IMP, CAS),
optimized the electromagnetic design of the HWR1
cavities within this superconducting linac, manufactured
a prototype, and tested it.

CAVITY DESIGNElectromagnetic Design
The design of the HWR1 seeks to achieve a balanced
compromise between optimal RF performance, adequate
mechanical properties, and ease of fabrication and surface
preparation. The initial focus is on optimizing the RF
properties of the HWR cavity, with the goal of minimizing
heat load and maximizing the accelerating gradient. Thisis achieved by targeting a higher R/Q0 (where R is theshunt impedance and Q0 is the unloaded quality factor), a
higher geometry factor (G), and lower peak surface fields(Bpk/Eacc and Epk/Eacc) to avoid field emission.
To achieve these objectives, the HWR1 is designed witha taper-shaped inner conductor and a ring-shaped drift
tube, which minimizes the peak surface fields. At the sametime, the outer conductor is kept cylindrical to ensure easeof fabrication. Two rinsing ports are opened on each side
to facilitate post-processing of the superconducting cavity.
The thicker port on the outer conductor is the coupling
port of the fundamental power coupler (FPC), and thethinner port on the opposite side is the signal extraction
port.
The final optimized RF parameters of the cavity arepresented in Table 1. And the cavity electromagnetic field
distribution are presented in Fig. 1.
Table 1: RF Parameters of HWR1
Parameters

Value

Unit

Frequency
βopt
Beam ApertureG
R/Q
Leff (βλ)
Ep/Eacc
Bp/Eacc
Cavity Diameter
Cavity Height

325
0.21
30.00
59
299.82
193.84
5.88
9.96
194
471

MHz
mm
ohmn
ohmn
mm
mT/(MV/m)mmmm___________________________________________* Work supported by Chinese Academy of Sciences “The Development ofHigh Stability Cryomodule [E129812YR0]”, National Key R&D "Nextgeneration heavy ion accelerator key components cooperation
development [E01O591KJ0]”.
†
Email: liangzehua@impcas.ac.cn‡
Corresponding author, Email: xumx@impcas.ac.cn
TUPB: Tuesday Poster Session
MC3.7 Superconducting structures

TUPB050
423

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DEVELOPMENT OF THE SUPERCONDUCTING HWR CAVITIESFOR NICA PROJECT

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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DESIGN AND IMPROVEMENT OF NORMAL CONDUCTINGHEAVY ION LINAC IN CHINA*
X.J. Yin†, Z.S. Li, Y.Q. Yang, H. Du, F. Ma, G.X. Li, Y. Cong, X.W. Xu, X.N. Li,C.C. Li, L. Jing,
H.N. Wang, P. Jin, X.J. Liu, C. Qian, W. Lu,W. Q. Yang, L.J. Mao, D.Q. Gao, J.X. Wu, J. Meng,
L.T. Sun, Q.G. Yao,W. Zhang, Z. Xu, J.C. Yang, Y.J. Yuan, Y. He, H.W. Zhao, J.W. Xia
Institute of Modern Physics, CAS, Lanzhou, China
Y.R. Lu, K. Zhu, X.Q. Yan
State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, China
Abstract
The research on heavy ion linac was began more thanten years ago initially to improve the HIRFL operation atIMP. In China, the first continuous wave (CW) heavy ion
linac,SSC Linac, working at 53.667MHz was developed as
the SSC injector. The ion particle can be accelerated to
1.48MeV/u with the designed A/q=5.17. At present stage,
this CW linac has been put into operation and the Uranium
has been accelerated to 1.48MeV/u successfully. To satisfy
the continue requirements, a compact 162.5MHz heavy ion
linac operating in pulse mode was developed. The “KONUS” beam dynamics design was adopted and the heavy
ions can be accelerated to 4MeV/u with A/q≤3. The SESRI
linac was another pulse machine which was built at Harbin.
In this linac, both of the heavy ions and proton beam canbe accelerated by this linac to 2MeV/u and 5.6MeV, respectively. In this paper, the status of these three heavy ion
linacs and their beam commissioning results were presented.

SSC LINAC
The SSC Linac is a CW heavy ion linac designed as the
new injector for the Separated Sector Cyclotron (SSC) at
IMP-HIRFL to improve the performance efficiency [1, 2].
The SSC Linac mainly consist of a super-conducting
electron-cyclotron-resonance ion source (SC-ECR),
a 4-rod RFQ, four IH-DTLs and four bunches, as shown in
Fig. 1. This linac was specifically designed to make use of
53.667 MHz which is four times of the SSC working frequency. For increasing the capture efficiency and longitudinal matching between linac and SSC, a pre-bunch working at 13.417 MHz was designed before the RFQ.The ion
particle with the ratio of mass-to-charge A/q≤5.17 can be
accelerated to 1.48 MeV/u. After then the particle can befurther accelerate to 15.53 MeV/u by SSC. The beam transmission of the linac is as high as 85%.

Key Components
Super-conducting Electron Cyclotron Resonance ion
source (SECRAL-I) is designed to operate at multiple microwave frequency with 28 GHz &18 GHz. It was upgraded from the existing magnet body of SECRAL and a___________________________________________* Work supported by NSF11375243† yinxj@impcas.ac.cn
TUPB051
426

Figure 1: Photo of the SSC linac.
new designed cryostat in 2019. In September 2023,
SECRAL-I was moved to SSC-Linac front-end replacing
the existing normal conducting ECR ion source to provide
highly charged ion beams, such as Uranium .
The CW 4-rod RFQ was design and fabrication under thecollaboration between IMP and Peking University [3, 4].
The particle with mass-to-charge ratios with ≤7 can be accelerated from 3.728 keV/u to 143 keV/u.
We adopt the IH-DTL as main accelerating section. The
Inter-digital H mode (IH-DTL) has a higher accelerating
efficiency because this structure has higher shunt effective
impedance and compact structure [5]. For our 53.667 MHz
heavy ion linac, the effective shunt impedance is about300-180 MΩ/m for the relativity factor between 0.020.05 especially. All measured Q0 values of DTL cavities areabove 85% of the simulation results by CST-MWS [6].
The SSC Linac was initiated to accelerate ion particles
to two inject energies using different operation mode. The
first mode is that 0.58MeV/u can be implemented using
DTL1&2. The second mode can be performed using DTL3
to 1.025 MeV/u. Then 5.97MeV/u and 10.2 MeV/u can beobtained from SSC for various experiments, respectively.
Based on the successful experience, the SSC linac was upgraded by adding DTL4 in 2022. Then the extracted energyof heavy ion form linac increase to 1.48 MeV/u. The HEBT
was also modified to match this upgraded.

Operation Status
In the September of 2019, the SSC Linac including
DTL1&2 was installed in the SSC hall and put into operation. The heavy ion particles, such as 78Kr13+, 129Xe22+,
209 32+
Bi , et.ac, with 0.58 MeV/u was successfully injected
TUPB: Tuesday Poster Session
MC3.2 Ion linac projects

.IOD dna ,rehsilbup ,krow eht fo eltit ,)s(rohtua eht ot noitubirtta niatniam tsum krow siht fo noitubirtsid ynA .)4202 ©( ecnecil 0.4 YB CC eht fo smret eht rednu desu eb yam krow siht morf tnetnoCSUPERCONDUCTING =0.40 HALF-WAVE CAVITY DESIGN FOR CiADS*
Z. H. Liang1,2†, M. Xu1‡, S. X. Zhang1, L. B. Liu1, J. Y. Wang1, Y. M. Chu1,2,3, H. Guo1, T. C. Jiang1,
S. C. Huang1, C. L. Li1, P. A. Xiang3, Q. T. Huang3, P. R. Xiong1, S. H. Liu1, T. Tan1, Z. J. Wang1,3,
F. F. Wang1, Y. He1
1
Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China
2
University of Chinese Academy of Sciences, Beijing, China
3
Advanced Energy Science and Technology Guangdong Laboratory, Huizhou, China
Abstract
A 325 MHz, optimal beta = 0.40 niobium half-wave
resonator(HWR)
called
HWR040forthesuperconducting driver linac of the China initiative
Accelerator-Driven subcritical System (CiADS) has been
designed and analyzed at the Institute of Modern Physics,
Chinese Academy of Sciences (IMP, CAS). The linac
requires 60 HWR040s to accelerate protons from 45 MeV
to 175 MeV. This paper mainly presents a design schemeof HWR040 and a new method of aluminum-niobium
composite with liquid helium partially immersed cavity.
Meanwhile,electromagnetic
field
optimization,mechanical structure design and heat transfer simulation
are carried out, to predict the behavior of the cavity underpractical operating process.

INTRODUCTION

increase beam energy spread, leading to operational
instability of the superconducting cavities.
When low-beta cavities operating in CW mode,
frequency detuning due to Lorentz forces does not varyover time, making pressure fluctuations in the helium theprimary factor affecting the stability of the cavity
operation. While tuners can partially compensate forfrequency shifts caused by helium pressure fluctuations,frequent tuner motor movements can introduce issues
such as electromechanical resonance. Therefore, it isessential to enhance the mechanical stability of the HWR,
through reducing their helium pressure sensitivity
coefficient to ensure that pressure fluctuations do notaffect the stable operation of the cavities under the current
cryogenic system conditions [2].
This paper proposes a method to solve these issues by
optimizing the electromagnetic design and utilizing an
aluminum casting technique to modify the surface
morphology of the superconducting cavity in contact withliquid helium. Based on this new concept, the Al/Nb
composite HWR040 has been designed.

The CiADS is a major scientific infrastructure currently
under construction in China. This system comprises threemain components: a high-current, high-powersuperconducting proton linac working in continuous wave
(CW) mode, a spallation target, and a subcritical reactor.
ELECTROMAGNETIC DESIGN
The proton beam generated by a proton source isLayout of RF Designtransmitted through a low energy beam transport line, an
RFQ, and a medium energy beam transport line before
Due to their complex structure, low and medium beta
entering the superconducting acceleration section. This
superconducting cavities are prone to field emission evensection consists of 9 HWR010s, 24 HWR019s,
after BCP surface treatment, particularly when the surface
60 HWR040s, 30 Ellip062s, and 28 Ellip082s cavities,
peak electric field (Epk) exceeds 30 MV/m. At the same
ISBN: capable
978-3-95450-219-6
ISSN:
2226-036610.18429/JACoW-LINAC2024-TUPB054
of accelerating a 5 mA protonbeam
to 630 MeV. doi: time,
to meet the requirements specified by the accelerator
The HWR040s section
cover
an energy
range of 45-IL, USA physics design,
32nd Linear
Accelerator
Conference (LINAC2024),Chicago,
JACoW thePublishing
operating Epk for the 325 MHz
175 MeV [1]. Given the high cost of cryogenic systems,
HWR040 cavity has been set at 28 MV/m. This cavity was
for CiADS to achieve commercial viability, the low-beta
designed and optimized using CST Studio Suite [3].
superconducting sections will need to operate at 4.2 K.
The electromagnetic design focused on minimizing the
However, at this temperature, the superconducting
Epk/Eacc and Bpeak/Eacc while maximizing (R/Q)*G ascavities are inevitably affected by the vaporization ofmuch as possible. To achieve this, the inner conductor of
liquid helium and vibrations from the cryogenic system.
the HWR040 was designed with a Tapper-type featuring a
The bandwidth of the superconducting cavity generally
larger opening. The main coupling port is located on thein the range of a few hundred hertz. Any deformations
sidewall of the cavity, and four cleaning ports arecaused by various disturbances can lead to frequency
positioned on the upper and lower end caps respectively,
shifts, or cavity detuning. If the detuning is significant andallowing high-pressure rinsing (HPR) water pipes toover the bandwidth of the cavity, it can cause a notable
extend deep into the cavity without significantly affecting
decrease in RF power delivery efficiency and may also
the electromagnetic field distribution. This ensures thatthe inner surface of the cavity can be thoroughly cleaned* Work supported by Chinese Academy of Sciences “The Development ofHigh Stability Cryomodule [E129812YR0]”, and the Large Researchduring the HPR process. The cavity vacuum model andInfrastructures “China initiative Accelerator Driven System [2017electromagnetic field distribution are presented in Fig. 1.
000052-75-01-000590]".
†
And Fig. 2 shows the transit time factor (TTF) curve of
Email: liangzehua@impcas.ac.cn‡
this cavity. Table 1 lists the main RF parameters of this
Corresponding author, Email: xumx@impcas.ac.cn
cavity.
___________________________________________

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB057

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MAXIMUM ENTROPY PHASE SPACE TOMOGRAPHY UNDERNONLINEAR BEAM TRANSPORT
L. W. Liu∗ 1,2,3 , Z. J. Wang1,2,3 , J. C. Wong1,2,3 , Y. Du1,2,3 , T. Zhang1,2,3 , H. Y. Zhou1,2,3 , B. H. Ma1,2,3
C. G. Su1,2,3 , M. Yi3 , L. Y. Gong1,2 , T.Y. Li1,2,3 , T. L. Wang1,2,3 , Y. M. Chu1,2,3
Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China
2
University of Chinese Academy of Sciences, Beijing, China
3
Advanced Energy Science and Technology Guangdong Laboratory, Huizhou, China
1

Abstract
Obtaining the complete distribution of a beam in highdimensional phase space is crucial for predicting and controlling beam evolution. Previous studies on tomographic
phase space reconstruction often required linear beam optics
in the relevant transport section. In this paper, we show thatthe method of maximum entropy tomography can be generalized to incorporate nonlinear transformations, thereby
widening its scope to the case of nonlinear beam transport.
The improved method is verified using simulation results
and potential applications are discussed.

INTRUDUCTION
Tomography is a general term for the reconstructionof a high-dimensional distribution using multiple lowdimensional profiles. The maximum entropy tomography
is to select the high-dimensional distribution with the maximum information entropy as the reconstruction solution
under the premise of satisfying the profiles. One characteristic of this method compared with other tomographymethods is that it can clearly identify the most suitable solution according to the principle of maximum entropy. A detailed discussion of maximum entropy theory can be foundin Ref. [1]. The previous use of the entropy-maximum
tomography method to reconstruct the four-dimensional
phase space distribution using two-dimensional profiles is
the Ref. [2]. In this paper, we extend the application ofentropy maximum tomography to nonlinear situation, sothat our reconstruction is no longer limited by the mapping
relationship between the directions where the profiles arelocated, and can accept the profiles without an upper limitof number. The position of the measured profile is called
the measurement point, and the position of the reconstructedresult is called the reconstructed point. In the following partof this paper, we discuss the entropy-maximum tomography
when the mapping between the distribution of reconstructed
points and the distribution of measured points is nonlinear.
In the part of simulation verification, we take the beam fromthe reconstructed point to the measurement point through a
sextupole with adjustable intensity as an example, and use 12
two-dimensional profiles of the measurement point to reconstruct the four-dimensional distribution of the reconstructed∗ liuliwen@impcas.ac.cn

TUPB057
434

point position. This work will certainly help to control the
motion state of the beam in the accelerator [3].

NONLINEAR MAXIMUM ENTROPYTOMOGRAPHY
For a four-dimensional distribution 𝜌(𝑥, 𝑥 ′ , 𝑦, 𝑦′ ) to besolved, its information entropy 𝐻[𝜌] is in the form Eq. (1).
Here we use the same form of four-dimensional information
entropy as in Ref. [2].
𝐻[𝜌] = − ⨌ 𝜌(𝑥, 𝑥 ′ , 𝑦, 𝑦′ ) ln 𝜌(𝑥, 𝑥 ′ , 𝑦, 𝑦′ ) 𝑑𝑥 𝑑𝑥 ′ 𝑑𝑦 𝑑𝑦′(1)
The 𝑗-th of the 𝑛 profiles measured is denoted as 𝑔(𝑢𝑗 , 𝑢𝑗′ ),which is a projection of the four-dimensional distribution
𝜌(𝑢𝑗 , 𝑢𝑗′ , 𝑣𝑗 , 𝑣𝑗′ ) on a two-dimensional plane (𝑢𝑗 , 𝑢𝑗′ ) andshould satisfy the constraint condition Eq. (2).
𝐺𝑗 = 𝑔(𝑢𝑗 , 𝑢𝑗′ ) − ∬ 𝜌(𝑓𝑗 (𝑥, 𝑥 ′ , 𝑦, 𝑦′ )) 𝑑𝑣𝑗 𝑑𝑣𝑗′

(2)

The 𝑓𝑗 in Eq. (2) represents the mapping from fourdimensional space (𝑥, 𝑥 ′ , 𝑦, 𝑦′ ) to four-dimensional space(𝑢𝑗 , 𝑢𝑗′ , 𝑣𝑗 , 𝑣𝑗′ ). This is a generalized mapping, which cantake any form that can be determined. (𝑢𝑗 , 𝑢𝑗′ , 𝑣𝑗 , 𝑣𝑗′ ) is an orthogonal four-dimensional space composed of the two axesof the plane in which we measure the 𝑗-th projection and theother two axes that are orthogonal to them.
Create a new function 𝐾[𝜌] with 𝑛 Lagrange multipliers
𝜆, where 𝑛 is the number of constraints.
𝑛𝐾[𝜌] = 𝐻[𝜌] + ∑ ∬ 𝜆(𝑢𝑗 , 𝑢𝑗′ )𝐺𝑗 [𝜌] 𝑑𝑢𝑗 𝑑𝑢𝑗′

(3)

𝑗=1

The 𝜌 that maximizes 𝐻[𝜌] is denoted by 𝜌∗ , and when 𝜌is 𝜌∗ , the partial derivative of 𝐻[𝜌] with respect to 𝜌 needs
to be 0.
𝑛𝜕𝐾[𝜌]⎜ln 𝜌∗ + 1 + ∑ 𝜆(𝑢𝑗 , 𝑢𝑗′ )⎞⎟ 𝑑𝑥 𝑑𝑥 ′ 𝑑𝑦 𝑑𝑦′
= −∭⎛
𝜕𝜌
𝑗=1
⎝
⎠
(4)
From Eq. (4), we can write the form of the solution for 𝜌∗ .
We can know that it is a four-dimensional function composedof 𝑛 two-dimensional functions multiplied together, and theplane in which these two-dimensional functions reside eachcorresponds to a different plane in which the projection
resides. We can rewrite it as Eq. (5). Where 𝐶 is someconstant that we don’t care about when we only take the
TUPB: Tuesday Poster Session
MC4.1 Beam diagnostics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA

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ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB058

A COMPARISON OF RMS MOMENTS AND STATISTICAL DIVERGENCES
AS WAYS TO QUANTIFY THE DIFFERENCE BETWEEN BEAM PHASESPACE DISTRIBUTIONSY. Du∗ ,1,2,3 , Z. J. Wang1,2,3 , J. C. Wong1,2,3 , L. W. Liu1,2,3 , C. G. Su1,2,3 , M. Yi3 , L. Y. Gong1,2 ,T. Zhang1,2,3 , H. Y. Zhou1,2,3 , B. H. Ma1,2,3 , Y. M. Chu1,2,3 , T. Y. Li1,2,3 , T. L. Wang1,2,3
1
Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China
2
University of Chinese Academy of Sciences, Beijing, China
3
Advanced Energy Science and Technology Guangdong Laboratory, Huizhou, China
Abstract
Accurately assessing the difference between two beam
distributions in high-dimensional phase space is crucial forinterpreting experimental or simulation results. In this paper,
we compare the common method of RMS moments andmismatch factors, and the method of statistical divergencesthat give the total contribution of differences at all points.
We first show that, in the case of commonly used initial
distributions, there is a one-to-one correspondence between
mismatch factors and statistical divergences. This enables us
to show how the values of several popular divergences varywith the mismatch factors, independent of the orientation of
the phase space ellipsoid. We utilize these results to propose
evaluation standards for these popular divergences, which
will help interpret their values in the context of beam phasespace distributions.

This is a symmetric matrix constituted by four second-ordermoments. Each Σ corresponds to a quadratic form RMS
phase ellipse equationx𝑇 Σ−1 x = 1,

where x = (𝑥, 𝑥 ′ )𝑇 is the 2D phase space coordinates of thebeam.
The mismatch factor measures the difference between
two ellipses in phase space that have the same center andarea but do not completely overlap. They both have theform of Eq. (2) and share the same RMS emittance. If one
ellipse can exactly enclose the other after being scaled by acertain proportion, then the mismatch factor is defined as
the value of this scaling factor minus 1. The commonly used
calculation formula is as follows [10]:1/2

Δ + √Δ(Δ + 4) ⎤𝑀 = ⎡⎢1 +⎥2⎣⎦

INTRODUCTION
In the research fields of beam transport line design, beamdiagnostics, phase space tomography and so on, accurately
assessing the difference between two beam distributions inhigh-dimensional phase space is crucial for interpreting experimental or simulation results [1–3]. A common approachto quantify these differences is through the use of RMS moments and mismatch factor, which gauges the overlap of
RMS boundaries [4]. Another more detailed approach is touse statistical divergences, which give the total contributionof differences at all points, commonly including: KullbackLeibler divergence, Jensen-Shannon divergence, Total Variation distance, Hellinger distance, collectively referred to as
f-divergence [5–9]. This paper compares these two different
methods, aiming to find the connection between them.

BASIC TERMS
RMS Moments and Mismatch Factor
Considering a beam distribution centered at the origin ofthe (𝑥, 𝑥 ′ ) phase space, if we conduct RMS statistics on it,
we can obtain the following covariance matrix:Σ=(∗ duyu@impcas.ac.cn

TUPB058438⟨𝑥𝑥⟩⟨𝑥 ′ 𝑥⟩⟨𝑥𝑥 ′ ⟩).
⟨𝑥 ′ 𝑥 ′ ⟩

(1)

(2)

− 1,

where
Δ = Δ𝛼2 − Δ𝛽Δ𝛾,

(3)
(4)

with Δ𝛼, Δ𝛽 and Δ𝛾 being the differences in Twiss parameters between the two phase ellipses.

f-Divergence
The f-divergence is a class of methods used to measure
the difference between two probability distributions, defined
as follows (1D):
𝐷𝑓 [𝑝(𝑥)||𝑞(𝑥)] = ∫ 𝑞(𝑥)𝑓 [

𝑝(𝑥)
] d𝑥;
𝑞(𝑥)

(5)

where 𝑝(𝑥) and 𝑞(𝑥) are the probability density functionsof two distributions. 𝑓 (⋅) is a convex function and satisfies
𝑓 (1) = 0. Different 𝑓 (⋅) correspond to different statistical
divergences. This paper selects four popular divergences tostudy the beam distribution, with corresponding forms andcalculation formulas are shown in Table 1.

THE RELATIONSHIP BETWEENMISMATCH FACTOR AND
F-DIVERGENCE
Theorem 1 In 2D phase space, there is a one-to-one correspondence between the f-divergence and the mismatch factor
for two beam distributions with elliptical symmetry.
TUPB: Tuesday Poster Session
MC4.1 Beam diagnostics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB060

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DEVELOPMENT OF AN X-BAND LLRF PROTOTYPE FOR THE
EUPRAXIA@SPARC_LAB LINAC*
P. D. Meruga†1, B. Baričevič, M. Cargnelutti, Instrumentation Technologies, Solkan, Slovenia
L. Piersanti, M. Bellaveglia, B. Serenellini, INFN - Laboratori Nazionali di Frascati, Frascati, Italy
A. Mostacci, Sapienza University of Rome, Rome, Italy1also at Sapienza University of Rome, Rome, Italy
Abstract
EuPRAXIA stands for “European Plasma Research Accelerator with eXcellence In Applications”. It's a next generation free-electron laser (FEL) aimed at developing acompact, cost-effective particle accelerator based on novel
wake-field accelerator technology. Traditionally, high-energy physics requires higher acceleration voltages, so developing the X-band acceleration technology, enables thepossibility to achieve high gradients with very compact
structures. The EuPRAXIA LINAC injector comprises one
S-Band and two X-Band sections, achieving a max beamenergy of 1 GeV. Low-Level Radio Frequency (LLRF) systems are crucial for RF station synchronization and machine stability at femtosecond precision. Currently, there
are no commercially available X-band LLRF solutions, especially for pulse processing and control in the 100 ns
range. This project aims to develop an X-band LLRF prototype, in collaboration with INFN, tailored to meet
EuPRAXIA@SPARC_LAB LINAC's demands. Once
confirmed on a real testbench, the prototype will be used
as a starting point for the industrialization into a commercial instrument. This paper presents the architecture andpreliminary results of the prototype.

INTRODUCTION
In recent years, the field of particle accelerators has witnessed significant advancements, driven by the need forcompact, cost-effective, and high-performance systems.
Among these innovations, the EuPRAXIA (European
Plasma Research Accelerator with eXcellence In Applications) project stands out as a pivotal initiative aiming to develop the world's first compact accelerator based on plasma
technology [1]. Within this framework, the SPARC_LAB
LINAC (Sorgente Pulsata e Amplificata di Radiazione Coerente_Laboratori Nazionali di Frascati Linear Accelerator) plays a crucial role.
The EuPRAXIA SPARC_LAB LINAC, housed at the
INFN-LNF (Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali di Frascati) in Italy, is designed to serve asa testbed for advanced acceleration techniques and beam
manipulation. Figure 1 shows the machine layout of the
SPARC_LAB LINAC combining the conventional radiofrequency (RF) linear acceleration that includes 1 S-band
RF gun, 4 S-band and 16 X-band RF structures with state___________________________________________* This project has received funding from the European Commission Horizon Europe Research and Innovation Programme under Grant Agreement
no. 101073480 and the UKRI guarantee funds.
† phanideep.meruga@i-tech.si
TUPB060442

of-the-art plasma acceleration, aiming to achieve unprecedented beam quality and energy efficiency.
The integration of these technologies is expected to address some of the fundamental limitations of traditional accelerators, such as size, cost, and energy consumption.

Figure 1: EuPRAXIA@SPARC_LAB machine layout [2].
A key component of this innovative system is the development of the X-Band Low-Level Radio Frequency(LLRF) system. The X-Band LLRF system is crucial for
precise control of the accelerating fields, ensuring stability
and high performance of the electron beam. Operating at
higher frequencies than traditional S-Band systems, the XBand technology offers significant advantages in terms of
reduced accelerator size and enhanced accelerating voltage
gradients in the order of 60 MV/m. This development is
instrumental in achieving the compact and efficient design
goals set by the EuPRAXIA project.
This paper provides a comprehensive overview of the
EuPRAXIA X-band LLRF prototype requirements, detailing the architecture of the prototype, the realization of the
prototype which includes the development and assembly.
The results from initial experimental runs, highlighting theprototype’s front-end performance in terms of amplitude
and phase stability are presented.

Requirements
The below Table 1 describes the EuPRAXIA X-band
LLRF prototype requirements that provides the input andthe starting point towards the development of the prototype. The main requirements are the prototype operates inpulsed mode at a carrier frequency of 11.994 GHz, with amaster oscillator input level of 0 dBm. It utilizes pulse
length of 100 ns and a greater than equal to 250 MHz sampling rate for precise control and signal processing. The
front-end should handle the input levels up to +20 dBm andrequire a bandwidth greater than 20 MHz to process the
100 ns pulses. The back-end should provide output level at+10 dBm with a rise time of 10-12 ns, maintaining signal
integrity. The system should have a low added amplitude
noise (0.01-0.05% RMS) and phase noise (0.01-0.015 degrees RMS) over 400 pulses, ensuring high signal fidelity.
With two RF input channels and one RF output channel, an
TUPB: Tuesday Poster Session
MC4.4 Low level RF32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB065

C. Baltador†, A. Palmieri, F. Grespan, A. Pisent
INFN – LNL Legnaro, Italy
Abstract
The normal conducting part of ESS LINAC in Lund
(Sweden) uses 5 DTL cavities, provided by INFN LNL as
in-kind partner, to accelerate 60 mA proton beam from3.62 MeV to 90 MeV. DTL1 have been tuned, installed in
the accelerator tunnel and RF conditioned in 2021-2022,
DTL2, 3 and 4 in 2022-2023, while DTL5 has been tuned
and installed in summer 2023, but not yet conditioned. All
the DTLs were equipped with tuning elements like tuners
and post couplers (PCs), but the challenges experienced
during the tuning of DTL1 has resulted in a change of tuning strategy, which effectively reduced the timeframe totune the other cavities from months to days. The aim of thispaper is to give an overview of the achieved results of tuning procedure performed on the DTLs.

INTRODUCTION
European Spallation Source (ESS) [1] is a proton linac
driven neutron source, under construction in Lund, Sweden. The last section of the normal-conducting part of thelinac feature a drift-tube linac (DTL), composed by fivetanks, provided by INFN LNL [2]. DTL tanks are composed by 4 stainless steel modules. Drift tubes (DTs) aredistributed along the tank, hold in place by vertical stems.
All DTL components suffer of mechanical tolerancesand despite the use of sophisticated alignment instrumentation, like laser trackers, relative alignment cannot be perfect. These mechanical imperfections, which can also beenhanced by thermal effects, cause random local change inthe capacitance of the DTL cells, moving the accelerating
field away from the reference one, defined to be the same
through all the gaps. To ensure optimal performance andaccurate acceleration of the beam to match the desired
beam dynamics, these perturbations must be compensatedwith a proper tuning of the cavity.

To tune the cavity, DTL tanks feature accordable elements (see left hand side of Fig. 1):• Tuners: make the cavity resonate at the correct frequency• Post couplers (PCs): stabilize the field with respect
to sources of local frequency detuning [3].
• Stubs: placed at PC tips make the accelerating field
uniform along the tank length.
In the case of ESS DTL, the number of tuners and PCs
are summarized Table 1. Note that the number of PCs of
Tanks 1 and 2 don’t match the number of DTs: the numberof PCs was chosen following a criterion of a sufficientnumber of post couplers per metre [4].
Table 1: Main Tank Parameters
Tank
1
2
3
4
5

DTs
60
33
28
26
22

Tuners
26
26
26
26
26

PCs
24
17
28
25
22

E0 [MV/m]
3.00
3.16
3.07
3.04
3.13

FIELD MEASUREMENT
The measurement of the accelerating field in the cavity
is carried out with usual bead pulling technique: by inserting a small diamagnetic bead, a volume change ∆𝑉 (perturbation) of the cavity is induced, which shifts the resonant
frequency 𝜔 . The bead can be driven through all the gapsof the DTL with a dielectric (nylon) wire, whose path isguided by a series of pulleys and moved by an electric motor. For ESS DTLs, a fishing line and an aluminium beadwere used.
By using a Vectorial Network Analyzer (VNA) to drive
low RF power into the cavity, frequency is locked and aphase shift ∆𝜑 rather than a frequency shift are recorded.
The two are related by the relation:
∆𝜑

− tan

𝑄

∗

−

∗

,

(1)

where 𝜔∗ is the frequency with the bead and 𝑄 is the‘loaded’ Q of the cavity. Bead perturbation is cancelled inside the DTs, giving a profile with peaks at the gaps andvalleys in the DTs. It is then possible to derive the 𝐸 fieldfrom the phase shift thanks to the Slater perturbation theorem [5].
By integrating the obtained 𝐸 field over the gap length
𝐿, the accelerating field 𝐸 is obtained for each gap:
Figure 1: Internal view of one DTL tank (left). A metallic
cylinder inserted in the last cell of the DTL to perturb thecavity (right). Tuners and PCs distribution along the DTL
Tank (down).

𝐸

𝐸 𝑧 𝑑𝑧 .

(2)

To reduce the noise coming from the measurements, it ispossible to integrate over the length 𝑙 of the bead, using thepeakfield method [6], which uses the theoretical field___________________________________________† carlo.baltador@lnl.infn.it
TUPB: Tuesday Poster Session
MC3.4 Proton linac projects

TUPB065
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TUNING OF ESS DTLs

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB066

D. Sertore∗ , M. Bertucci, A. Bosotti, E. Del Core, F. Fiorina, L. Monaco, R. Paparella, P. Spruzzola
INFN Milano - LASA, Segrate, Italy
1
C. Pagani , Università degli Studi di Milano, Segrate, Italy1also at INFN Milano - LASA, Segrate, Italy
Abstract
INFN Milano - LASA recently concluded its in-kind contribution to European Spallation Source Eric, providing the36 Superconducting Medium Beta cavities that will allow
boosting the proton beam energy from 216 MeV to 571 MeV.
The performances of the last four cavities, treated with
Electro-Polishing as main processing step, are presented
and compared with the results obtained on the remaining
cavities treated with Buffered Chemical Polishing. The overall performance of the delivered cavities and lessons learned
during the cavities production stages are also discussed.

INTRODUCTION
INFN Milano - LASA has taken on the responsibilityof the Italian In-Kind contribution to the European Spallation Source (ESS) ERIC, specifically in the development of
the Superconducting (SC) Medium Beta Cavities. We havedeveloped the electromagnetic design for these cavities, optimizing it with consideration of mechanical requirements,
industrial feasibility, and adherence to the ESS interface
requests. The importance of this last point should not be
underestimated, as it has been instrumental in ensuring aseamless assembly of the cavities in their cryomodule at
CEA Saclay. The key parameters of the INFN Medium Beta
cavities are summarized in Table 1.
Table 1: ESS Medium Beta Cavities Main Parameters
Parameter
Riris
Geometrical 𝛽
𝜋-mode Frequency
Acc. length
Cell-to-cell coupling k𝜋-5𝜋/6 mode sep.
Geometrical factor G
Optimum beta, 𝛽𝑜𝑝𝑡
Max R/Q at 𝛽𝑜𝑝𝑡
Eacc at 𝛽𝑜𝑝𝑡
Epeak /Eacc
Epeak
Bpeak /Eacc
Q0 at nominal gradient
Qext

Value
50 mm
0.67
704.42 MHz
0.855 m1.55 %
0.70 MHz
198.8 Ω0.705
374 Ω
16.7 MV/m
2.55
42.6 MV/m
𝑚𝑇
4.95 𝑀𝑉/𝑚>5 × 109
7.8 × 105

In the SC linac, the Medium Beta (𝛽=0.67) cavities willintercept the 62.5 mA proton beam from the Spoke section∗ daniele.sertore@mi.infn.it

TUPB: Tuesday Poster Session
MC3.4 Proton linac projects(256 MeV) and accelerate it to 571 MeV, preparing it for
injection into the High Beta cryomodules. These modules
will then boost the beam to its final energy of 2 GeV.
The 5 MW average power proton beam will operate inpulse mode at 14 Hz, with each pulse lasting 2.86 ms. Thelong beam pulse operation was a significant factor in the
project decision to use superconducting cavities, as it allows us to achieve the project parameters while maintaining
cost-effectiveness. Furthermore, there is a pressing need tooperate the cavities at a high accelerating gradient to attainthe required energy within the projected accelerator footprint. Upon reaching the target station, the proton beam will
generate a neutron beam through the spallation process [1].
Once operational, the European Spallation Source ERIC is
set to become the world’s most intense neutron source [2].
This paper provides an update on the status of cavity
production, with a particular focus on the recovery actions
undertaken to qualify cavities that were initially performing
below expectations, incorporating lessons learned during
the recovery process.

CAVITY PRODUCTION AND TESTING
The ESS Medium Beta cavities production is based on the“build to print” schema inherited from our previous work forEuropean XFEL SRF cavities [3, 4]. To ensure high quality,
strict guidelines for cavity production and a comprehensive
Quality Control and Quality Assurance plan are enforce
during the entire cavity production process [5].
Based on the ESS requirements, we have chosen to treat
the cavities using a Buffered Chemical Polishing (BCP)
process, both in bulk and as a final treatment. The final
treatment, known as the “Final BCP”, is part of the cavity preparation necessary to assemble the cavity before the
Vertical Test at cryogenic temperatures, required for cavity
qualification. To accommodate the high cavity delivery raterequired by the project, most of the qualification tests wereconducted at DESY, utilizing the AMTF infrastructure [6].
However, for specific cavities, we utilized the LASA infrastructure, which is not able to sustain the series test rate
but is equipped with advanced diagnostic tools capable ofidentifying quench and field emission sources that could
potentially limit the cavity performance [7].
A total of thirty-two cavities met ESS specifications, while
the last four, with lower performance, were accepted by the
project and installed in the first cryomodule, where beam
matching from the Spoke section to the elliptical section
requires less demanding acceleration fields. All the cavities were subsequently integrated into cryomodules at CEA
TUPB066
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INFN LASA IN-KIND CONTRIBUTION TO ESS ERIC PROJECT

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB067

F. Grespan, C. Baltador, L. Bellan, M. Campostrini, M. Comunian, E. Fagotti, L. Ferrari,
A. Palmieri, A. Pisent, C. Roncolato, INFN- LNL, Legnaro, Italy
D. Nicosia, L. Page, R. Zeng, ESS, Lund, Sweden
L. Y. Gong, IMP, Chinese Academy of Sciences, Lanzhou, China
F. Cismondi, F. Scantaburlo, IFMIF/EVEDA Project Team, Rokkasho, Japan
A. De Franco, QST, Rokkasho, Japan
H. Kobayashi, KEK, Tsukuba, Japan
Abstract
The performances and failure cases of the power couplers of the IFMIF/EVEDA RFQ and ESS DTLs have been
analysed with dedicated high-power test campaigns andMulti-Pacting (MP) simulation methods. The paper presents test and simulation methodology, results, and inputs
for the next activities.

INTRODUCTION

finding O-rings melted, once reached 60% average power.
In the same inspection the alumina was found coloured, as
well as the copper inner conductor (Fig. 2). Nonetheless, inNovember 2023, after reaching 25% average power, a vacuum leak occurred again.
An experimental and theoretical analysis of the electron
activity in the couplers was carried out to clarify the powerheat source capable to heat the O-ring at melting temperature (180°C).

IFMIF/EVEDA RFQ power couplers
Eight tetrode RF amplifiers at 175 MHz - numbered
1A…4A, 1B … 4B - feed the IFMIF/EVEDA RFQ [1] for
1.6 MW total power capability. The net power need is
1.3𝑀𝑊
𝑃 650𝑘𝑊𝑃
650𝑘𝑊 . Beam𝑃
performances in pulsed mode have been demonstrated in2019 [2]. In RF conditioning beam loading is absent, so
each coupler operates with PREV≈13%. The couplers(Fig. 1) are coaxial magnetically coupled loops, withoutbias. A coaxial planar alumina window separates vacuum
from air, vacuum sealing being provided by Viton O-rings.
The impedance matching between window and line isgiven by reducing the inner conductor radius. RF windows
are coated with 1.5 -3 nm TiN layer. The alumina is notdirectly water cooled. The couplers have been designed
and tested on a test cavity at full power (200 kW-CW) at
INFN-LNL in 2015 [3].

Figure 2: Status of “cold” (left) and “hot” (right) coupler.

ESS DTL’s Power Couplers
One 2.9 MW klystron at 4% duty cycle feeds each of the
2.2𝑀𝑊
5 DTLs (352 MHz). The net power need is 𝑃
𝑃
1.1𝑀𝑊 , coupled to the cavity
𝑃 1.1𝑀𝑊by 2 iris couplers placed on the bottom of the DTLs. The
air-vacuum separation between cavity and wave guide isprovided by a pillbox-type alumina RF window, water cooled and coated with 2 nm TiN layer. Windows are connected to the coupler box with a WR2300 HH flange (Fig. 3).
The windows have 2 view ports (air and vacuum sides).
The sealing between the RF window and coupler box is an
EPDM gasket, without RF joint protections. The RF windows were tested to full power in 2020.

Figure 1: Sketch of the IFMIF coupler. The diagnostics andthe positions of Viton O-ring are shown.
During RFQ RF conditioning operations toward CW [4](2019-2023), 5 of the 8 couplers showed anomalous temperature increases of the external conductors. Two improvements of cooling capability have been implemented: in2019 water jackets were applied on the external conductor.
In 2023 the inner conductor cooling was improved, after
TUPB: Tuesday Poster Session
MC4.6 RF power sources and power couplers

Figure 3: One of the ESS DTL RF windows. Brown coloration melted O-ring and light is shown.
In 2023 DTL1-2-3-4 started high power RF operation at
ESS Lund, reaching full performances [5]. But, after 6
weeks of operations, light started on both vacuum and air
TUPB067
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RF AND MULTIPACTING ANALYSIS OF THE HIGH-POWER COUPLERS
OF IFMIF/EVEDA RFQ AND ESS DTL

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB068

F. Grespan†,1, C. Baltador, L. Bellan, M. Comunian, M. Montis, A. Palmieri, A. Pisent
INFN-LNL, Legnaro, Italy
T. Bencivenga, P. Mereu, C. Mingioni, M. Nenni, E. Nicoletti, INFN-Torino, Torino, Italy
B. Jones, Y. Levinsen, R. Miyamoto, N. Milas, L. Page, C. Plostinar, R. Zeng, ESS, Lund, Sweden
1
also at ESS, Lund Sweden
The Drift Tube Linac (DTL) for the European Spallation
Source (ESS ERIC) will accelerate proton beam up to
62.5mA peak current from 3.62 to 90 MeV. The 5 cavities
are now fully installed and tested in the linac tunnel. Moreover, in 2023 DTL1 to DTL4 have been RF conditioned tofull power and beam commissioned with max peak current
at short pulses. Relevant results of these activities are presented in this paper.

INTRODUCTION
Status of Installation.
A total of 5 cavities of the Drift Tube Linac (DTL5) for
the European Spallation Source (ESS ERIC) were installedin September 2023 (Fig. 1), following completion of beamcommissioning at 74 MeV [1]. Tests were undertaken for
vacuum leaks, alignment, and the RF parameters werevalidated. The assembly of RF windows and power
couplers was completed in May 2024, after the high-power
tests reported in Ref. [2]. The DTL5 is now connected tothe cooling skid and ready for a series of integrated tests
scheduled before high power conditioning in November2024.

with Post Couplers (PCs) equipped with stubs is extensively described in Ref. [4]. The adjustable aluminium tuners and PCs are replaced with machined copper parts andcavity parameters are recorded (Table 1, Fig. 2).
Table 1: DTL5 RF Parameters (VNA Measurements)

DTL5

Abstract

Parameters
Freq. [MHz]DesignCoupl. factor [β]Q0 (SFish/1.25)
E0 flatness [%]Tilt.Sens.

1.84
43415
±2
N.A.

352.21

Measured352.266 (in vacuum,no RF power, 18°C)
1.95
43307
±1.15
±4.5 %/MHz

Figure 2: E0, gap-gap phase error and DT transverse alignment of DTL5.

“As Built” Simulations

Figure 1: The 5 DTLs now installed in the ESS tunnel.
DTL5 comprises 23 cells, i.e., 22 drift tubes (DTs). The
installation of DTs on the modules and module-to-module
assembly follows the sequence described in Ref. [3]. Eachassembly step is monitored with a laser tracker and leaktested. The total DT transverse errors specifications are±0.1 mm, and take into account the machining errors of
DTs and girders, and the positioning errors of DTs in themodules, the PMQs inside DTs and module-module alignment. Transverse PMQ alignment is within specifications(±0.1 mm) with the only exception of the high energy end
plate. Longitudinally, the maximum gap-gap error is < ±0.3mm, with the corresponding phase errors within the tolerance (< 0.5 deg). The process of tuning and stabilization
TUPB: Tuesday Poster Session
MC3.4 Proton linac projects

The data in Fig. 2, together with the data of DTL1-2-3-4[5], are the inputs for the beam dynamics “as built” model.
The simulation run with nominal current, 62.5 mA andnominal input beam rms emittances, 0.28/0.28/0.39
mm mrad. Steerers are activated to counteract PMQ misalignments, the max used steerer strength is 1 mT*m, withmax possible strength 1.4 mT*m. The run is without losses
with ou¬tput emittances comparable with nominal case(Fig. 3).

Figure 3: Nominal and “as built” DTL’s emittances.
TUPB068
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ESS DTL: FINAL INSTALLATION AND FIRST COMMISSIONINGRESULTS UP TO 74 MeV

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB069

G. Torrisi∗ , G. S. Mauro and G. Sorbello2 , INFN-LNS, Catania, Italy
A. Curcio, L. Faillace and B. Spataro
INFN Laboratori Nazionali di Frascati, Italy
L. Giuliano5 , M. Migliorati5 , A. Mostacci5 and L. Palumbo5
SBAI, Sapienza University of Rome, Italy2also at University of Catania, Catania, Italy 5 also at INFN-Sezione di Roma, Italy
Abstract
In this paper, the design of a compact C-band SLED RF
Pulse Compressor for a Very High Electron Energy (VHEE)FLASH machine is presented. A spherical cavity RF pulse
compressor - selected because of its compactness and relative ease of fabrication - is adopted to compress the 5 𝜇s
RF pulse, down to 1 𝜇s obtaining a peak power gain greaterthan 5. Both the RF and thermo-mechanical design havebeen carried out, including a sensitivity study to evaluate
the mechanical tolerances, possible tuning methods, and thecooling system. The main parameters of the full RF design(spherical storage cavity + mode converter/polarizer) andthe final mechanical design of the structure are presented.

velopment of a high gradient C-Band FLASH linac demonstrator is ongoing to test and validate all the C-Band key
components necessary for a VHEE Linac (see Fig. 1).

INTRODUCTION AND MOTIVATIONThis paper presents the complete design of a C-band(5.712 GHz) spherical pulse compressor for a Very HighElectron Energy (VHEE) FLASH machine. VHEE [1] irradiations could represent a valid technique to apply the
FLASH effect [2] in clinical use to treat deep tumors. The
design strategy and electromagnetic characteristics of the
C-band linac for VHEE FLASH radiotherapy is presented in[3]. The translation of FLASH therapy - a novel cancer treatment technique, aims to control the tumor-grown sparing
the healthy tissue from radiation damage increasing the therapeutic index - into clinical practice, especially for treating
deep-seated tumors, necessitates achieving Very High Electron Energy (VHEE) levels within the 50-150 MeV range [4,5]. The output beam energy can be increased by enhancing
the RF peak power at the expense of RF pulse width by using a pulse compressor. This system called “SLAC Energy
Doubler (SLED)”, firstly proposed and applied in [6], hasbeen widely used elsewhere according different schemes
such as the Binary Pulse Compression (BPC) [7], SLED-II[8], Barrel Open Cavity (BOC) pulse compressor [9] andsingle spherical cavity pulse compressor [10]. The latteris also the one selected for this work: it is composed ofa “special” 3 dB coupler (also acting as a circular polarizer) and a single spherical energy storage cavity (comparedwith the traditional SLED where two cylindrical cavities are
adopted).
At La Sapienza University of Rome, in collaboration with
the Italian Institute for Nuclear Research (INFN), the de∗ giuseppe.torrisi@lns.infn.it

TUPB: Tuesday Poster Session
MC4.7 Room temperature RF

Figure 1: VHEE FLASH linac general layout [3].

DESIGN OF THE SPHERICAL PULSECOMPRESSOR
A spherical cavity RF pulse compressor – selected because of its compactness and relative ease of fabrication –is adopted to compress the RF pulse obtaining a peak power
gain greater than 5. The spherical cavity pulse compressor,
visible in Fig. 2 (b), is composed of a 3 dB coupler (also acting as a circular polarizer, converting the input TE10 mode
into two, 90-deg shifted, circular TE11 output modes) and asingle spherical energy storage cavity. These two subsystems
have been firstly designed separately and then assembled
together to obtain the complete device. For the spherical cavity, two degenerated TE114 (see Fig 2(b)) have been chosen
as operating modes because of their high unloaded quality
factor, 𝑄0 = 134 × 103 .

RF Design and Tuning
The simulated S-Parameters of the pulse compressor by
CST Frequency Domain Solver are shown in Fig. 3. The
minimum value of |𝑆21 | is about −2 dB at the frequency
𝑓0 = 5.712 GHz. The corresponding coupling coefficient 𝛽
is calculated to be about 8.
TUPB069
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DESIGN AND OPTIMIZATION OF A C-BAND RF PULSE COMPRESSORFOR A VHEE LINAC FOR FLASH RADIOTHERAPY

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB070

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

R&D ON SRF AT INFN LASA
L, Monaco†, M. Bertucci, M. Bonezzi, A. Bosotti, E. Del Core, F. Fiorina, R. Paparella, D. Sertore,
P. Spruzzola, INFN Milano LASA, Segrate, Italy
C. Pagani1, Università degli Studi di Milano, Segrate, Italy1also at INFN Milano - LASA, Segrate, Italy.
Abstract
Sustainability and cost reduction are key factors for thedevelopment of future large particle accelerators. This motivated INFN LASA to initiate an INFN-funded R&D program dedicated to improving the performance of SRF Nb
cavities in terms of quality factor (High-Q) and accelerating gradient (High-G).
The R&D program will start by exploiting state-of-theart surface treatments on 1.3 GHz single-cell prototypes, inview of a possible industrialization process for large-scale
productions.
Integrating part of this program is the upgrade of our vertical test facility to enable qualification of such high-performance cavities. Ongoing activities include the construction of a new dedicated cryostat, which minimizes Liquid
Helium consumption, reduces the impact of trapped magnetic flux and provides a wide range of diagnostics forquench, field emission, and magnetic flux expulsion studies.

INTRODUCTION
The SRF group of INFN Milano - LASA has a long experience in the field of niobium (Nb) superconducting (SC)cavities and related accessories, with research and development activities also dedicated to the industrialization ofthis technology aimed at in-kind contribution to international projects such as E-XFEL, ESS and, recently, PIP-II[1-4].
Maintaining and reinforcing this excellence and expertise is important in view of future high-performance accelerators (such as lepton colliders and light machines) that
aim for even better performance for SRF cavities to meetgreater sustainability, cost reduction and short footprint (asfor example stated by the ESPP - European Strategy for
Particle Physics) [5]. Therefore, R&D programs dedicatedto the study and improvement of cavity surface and thermal
treatments to achieve High-Q and High-G performance
prove to be crucial activities.
The demonstration of how this approach is shared bymany worldwide parties is supported by similar 3-4 years
programs financed not only nationally as by INFN (withmain focus on future projects as ILC, Muon Collider, FCC,etc.), but also by international collaboration as ITN (ILC
Technology Network) that aim to reach High-G with good
Q0 at the ILC goal [6]. In this context, FCC is aiming for
20 MV/m with 3E10 while ILC expects 31.5 MV/m with
1E10 in operation. In particular ITN, that is still under formal finalization between all the partners, is a worldwide
technology network that aims to study some critical aspects___________________________________________† laura.monaco@mi.infn.it
TUPB070464

highlighted in IDT (ILC Development Teams) during the
preparatory phase of ILC. For ITN, INFN contributes to
SRF themes (cavities, cryomodules and ancillaries) working with our colleagues from EU labs involved and coordinated by CERN. Among the various tasks, we will takecare of the development and optimization cavities treatments, of their industrialization, and we will work on theharmonization of the EU/US pressure vessel code (PEDand ASME) with the Japanese HPGS (High Pressure Vessel Code), that will allow installing up to two European
cavities in the demonstrator cryomodule that it will assemble at KEK. This activity is important in view of the futureinternational projects where it will be essential to haveworld-wide contributions compliant with local regulations.
Furthermore, a four-year EAJADE EU Marie Curie program plays a crucial role in these activities since, sponsoring staff exchange between young EU researchers andwell-known labs and universities in US and Japan, will enrich and improve the knowledge exchange in the SRF
fields.

OUR R&D STRATEGY
The strategy we propose consists of an R&D phase basedon single cells at 1.3 GHz (reference frequency for these
activities) for the development of treatments that allow theHigh-Q to be extended towards the high gradient. Oncethese treatments will be consolidated, an essential step willbe their transfer to multicell cavities in view of a possible
large-scale production. This activity is synergic with the
SRF group's current program towards future colliders(ILC, Muon Collider, FCC, etc.).
Moreover, the R&D activities here described, in particular the High-Q part, will be synergic and it will profit of the
on-going developments and studies in our group for the optimization of the 650 MHz (1st sub harmonic of 1.3 GHz)PIP-II cavity treatments, that asks to reach a very high Q0
but at modest accelerating gradient.
Within our reference time frame (3-4 years), the plan fordeveloping the activities we propose, based on 1.3 GHz
technology, can be summarized in:• High-Q/High-G recipe development on 2 single-cellcavities. This activity will start from baseline process(E-XFEL like) and then it will include further treatments such as two-step baking, mid-T baking, etc.
Moreover, we will test the cavities not only at LASA
but also in other laboratories (i.e. CEA) for performance cross-check.
• Transfer of selected treatments to multicell, with 2 9cells, addressing the industrialization and QA/QC process implementation in preparation for a future largescale production.
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DESIGN AND TEST OF C-BAND LINAC PROTOTYPESFOR ELECTRON FLASH RADIOTHERAPY
L. Giuliano∗ , E. Anelli, E. Chiadroni2 , M. Coppola, A. De Gregorio1 , L. Ficcadenti1 , S. Farina1 ,D. Francescone1 , G. Franciosini1 , M. Magi1 , M. Migliorati1 , A. Mostacci1 , L. Palumbo1 , V. Patera1 ,F. Perondi, R. Remetti, A. Sarti1 , Sapienza University of Rome, Italy
D. Alesini, F. Cardelli, M. Carillo, A. Curcio, R. Di Raddo, L. Faillace, G. Franzini, A. Gallo,
L. Piersanti, B. Spataro, A. Vannozzi, INFN - LNF, Frascati, Italy
G. Cuttone, G. S. Mauro, G. Sorbello, G. Torrisi, INFN - LNS, Catania, Italy
M. Di Francesco, G. Felici, SIT - Sordina IORT Technology Spa, Aprilia, Italy1also INFN-Roma, Italy2also INFN-LNF, Italy
Abstract
FLASH Therapy [1], a novel cancer treatment technique,aims to control the tumor-grown sparing the healthy tissue
from radiation damage, increasing the therapeutic index.
Translating FLASH therapy into clinical practice, especiallyfor treating deep-seated tumors, necessitates achieving VeryHigh Electron Energy (VHEE) levels within the 50-150 MeV
range [2]. In the framework of the SAFEST project [3–7],
Sapienza University, in collaboration with INFN, is actively
developing a compact C-band linac demonstrator at the energy of 24 MeV (loaded) with a 100 mA peak current. This
paper provides insights into the design strategy and electromagnetic characteristics, focusing on prototype testing andtuning conducted at the Sapienza Accelerator Laboratory.
The progress of this innovative linac represents a step toward realizing an advanced FLASH VHEE source in cancer
treatment.

adapt these linacs for the treatment of deep-seated tumors
using Very High Energy Electron FLASH radiotherapy.
At La Sapienza University of Rome, in collaboration with
the Italian Institute for Nuclear Research (INFN), we are developing a high gradient C-Band (5.712 GHz) FLASH linac
demonstrator [8] with the aim of testing all key components
necessary for a VHEE Linac (Fig. 1). The first stage of thedemonstrator consists of a compact Standing Wave (SW)bi-periodic structure operating in 𝜋/2 mode followed by ahigh-gradient traveling wave (TW) structure, with a phaseadvance of 23 𝜋, intended to accelerate the electron beam up
to 24 MeV (loaded with 100 mA pulse current), the maximum energy being limited by radio-protection constraints
in the University laboratory.
In this paper, we present the status of the design andconstruction of the prototype which has to deliver ultra-highdose rate (UHDR) pulses typical of the FLASH regime [9],as reported in Table 1.

INTRODUCTION

Table 1: Most Used Parameters for FLASH Irradiation

FLASH radiotherapy (RT) has attracted significant attention within the cancer research community due to its
potential to effectively treat tumors while minimizing damage to surrounding healthy tissues. Preclinical studies haveshown that delivering electron radiation in extremely shortbursts (less than 100 ms) at ultra-high instantaneous dose
rates (exceeding 106 Gy/s) can significantly reduce toxicity in healthy tissues while maintaining therapeutic efficacy
against cancer.
The first experiment involving FLASH-RT was conductedby V. Favaudon and his team at Institut Curie in 2014 [1].
Since then, various in-vivo and in-vitro radiobiological studies have reported substantial sparing of normal tissues, nevertheless, more research is necessary to fully comprehend theadvantages and limitations of FLASH-RT and to identify thebest clinical applications. Currently, only a limited numberof dedicated electron linacs are employed for experimental
research, with ongoing studies and technological advancements aimed at developing more compact and cost-effective
linacs for high-energy electrons. The ultimate goal is to∗ lucia.giuliano@uniroma1.it

TUPB071
468

Symbol
PRF
𝑡𝑝
𝑡𝑖
𝐷̇
𝐷𝑝̇
𝐷𝑝

Description
Pulse repetition frequency
Electron pulse width
Total irradiation time
Time-averaged dose rate
Dose-rate in a single pulse
Dose in a single pulse

Value> 100 Hz
0.1-4.0 µs< 100 ms
> 100 Gy/s
> 106 Gy/s
> 1 GyThe facility will offer an adaptable platform for conducting
radiobiology experiments using both in-vitro and in-vivo
samples, and it will support the development and testing ofinnovative devices for precise measurements and monitoringof electron beam parameters in FLASH conditions.

FACILITY PARAMETERS AND LAYOUT
The proposed basic system (Fig. 1) is composed of astanding wave injector and a traveling wave accelerating
structure. A continuous electron beam of about 220 mA
is generated by a DC gun with a pulse length of 1 µs. The
accelerating structures are powered by a 5 MW klystron withan RF pulse length of 5 µs. The klystron output feeds a pulse
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FAST CHOPPER LINE FOR DONES
M. D’Andrea†, L. Bellan, L. Ferrari, F. Grespan, A. Palmieri, A. Pisent, INFN-LNL, Legnaro, Italy
M. Di Giacomo, GANIL, Caen, France
Abstract
The International Fusion Materials Irradiation Facility –DEMO-Oriented Neutron Early Source (IFMIF-DONES)
will provide a deuteron beam of unprecedented intensity
for irradiation and characterization of materials to be usedin fusion reactors. In recent years, the possibility to use asmall fraction of this beam for other applications in parasitic mode was discussed. This has the potential to not only
enlarge the user community without perturbing the main
operation, but also allow characterization measurements
for beam quality management purposes. Considering various requirements and constraints, the most promising option for the extraction towards such a parasitic line involves
the use of a meander-line travelling-pulse beam deflector
at the start of the High Energy Beam Transfer (HEBT) line.
This paper describes preliminary studies aiming at a first
definition of the structure, materials and geometrical parameters of the meander-line deflector.

INTRODUCTION
The definition of which materials shall be used for theconstruction of nuclear fusion reactors is a crucial part of
the European roadmap towards fusion electricity. To bevalidated and qualified, these materials must be exposed toneutron irradiation comparable to what is expected in a fusion reactor. The construction of IFMIF-DONES (referred
to as DONES in the following for simplicity), the staged
version of a facility capable of producing neutrons with therequired energy spectrum and fluence, was launched in
March 2023 in Escúzar, Spain, as part of the European Fusion Roadmap. The neutron flux (1018 neutron/m2/s) will
be produced by a deuteron beam accelerated to 40 MeV
hitting a liquid lithium target. The main parameters of the
DONES accelerator systems are reported in Table 1. Moredetails on the facility can be found in [1–4].
Table 1: Main DONES Accelerator Nominal Parameters
Particle
Peak current [mA]
Beam energy [MeV]𝛽Beam power [MW]RF frequency [MHz]

D+(p)
125
40 ± 5 FWHM
0.204
5
175

In the past years, the possibility to extract a small fraction of the beam and devote it to different applications (e.g.
physics experiments or beam characterization), without
perturbing the main operation, was discussed. Preliminary
explorations of this concept determined that it is particularly interesting if 1 bunch over 1000 of the fully accelerated 40 MeV beam can be extracted keeping the 125 mA___________________________________________† marco.dandrea@lnl.infn.it
TUPB073472

peak current intact. The bunch separation must therefore
take place after the full acceleration is completed, i.e. in the
HEBT. The most promising solution to achieve this setup
involves the use of a meander-line travelling-pulse beam
deflector to separate the selected bunch, coupled with electrostatic and magnetic septa to complete the extraction.

PRELIMINARY STUDIESIn a meander line beam deflector, a travelling electricfield pulse is applied between two electrodes around thebeam. If the rise/fall time and length of the impulse areproperly set, the electric field will act only on a selectedbunch, without perturbing the path of the others. However,the propagation speed of the signal along the beam trajectory must be reduced to be synchronized to the selectedbunch. For this purpose, the electrodes can be meandershaped, as already done in various facilities [5–7].
Preliminary investigations were carried out to identify asuitable location in the HEBT (shown in Fig. 1) for the installation of the meander line [8]. This is mainly driven by
the minimum achievable rise/fall time, as this puts a hard
limit to the bunch-by-bunch separation if the rest of thebeam must remain untouched. Since there is no longitudinal focusing, and therefore the beam increases its phasespread as it travels along the line, the separation must takeplace at the beginning of the HEBT. Considering a minimum achievable rise/fall time of 2-3 ns [9, 10], the suitableregion is restricted to the first 3.5 m of the line. Simulations
performed with TraceWin [11] for a typical DONES bunchshow that all particles are contained within 1.77 ns [8].
Therefore, an electric field pulse with a 2 ns plateau wasconsidered for the preliminary design.

Figure 1: Sketch of the DONES HEBT [12]. The region
considered for the installation of the meander-line deflector
is highlighted in red.

MEANDER LINE DESIGN
Several different solutions for the meander-line deflector
design were conceived [8]. The one considered in the following includes a total of three separate meander sections
installed in succession, followed by dedicated septa tocomplete the separation of the bunch. The main parametersof this setup are reported in Table 2.
The design of a meander line is driven by the synchronization between the electric field pulse along the line andthe bunch to be deflected. This depends also on the dielectric material chosen to separate the line conductor from the
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STATUS OF THE INFN LASA IN-KIND CONTRIBUTIONTO PIP-II PROJECT
R. Paparella†, M. Bertucci, M. Bonezzi, A. Bosotti, E. Del Core, F. Fiorina, L. Monaco, D. Sertore,
P. Spruzzola, INFN Milano LASA, Segrate, Italy
C. Pagani1, Università degli Studi di Milano, Segrate, Italy1also at INFN Milano - LASA, Segrate, Italy
H. Park, G. Wu, J. Ozelis, Fermilab National Accelerator Laboratory, IL USA
Abstract
The status of INFN LASA in-kind contribution to the
PIP-II project at Fermilab is reported in this paper. The effort for the series production of the 38 INFN LASA designed, 5-cell cavities with beta 0.61 for the LB650 sectionof the linac commenced and the status of ongoing activities
and major procurements is here conveyed. At the sametime, preliminary tests on INFN LB650 cavity prototypes
are progressing in order to optimize the complete preparation and qualification cycle. All cavities will be produced,
and surface treated in industry to reach the unprecedented
performances required, qualified through vertical cold test
at state-of-the art infrastructures and delivered as installation ready at the string assembly site.

INTRODUCTION
The Fermilab Proton Improvement Plan II (PIP-II) Linac
is designed to deliver a 1.2 MW H- beam upgradable tomulti-MW to enable LBNF and DUNE neutrino physics
projects [1]. The 800 MeV beam will be injected into theupgraded Booster Ring via a linac-to-booster transfer line
and it will then proceed to the Main Injector Ring.
The PIP-II linac features a flexible time structure for its
0.55 ms, 2 mA beam pulse in order to satisfy different experimental needs, with radiofrequency (RF) components
capable of supporting continuous-wave (CW) operations.
A key section of the linac is the 650 MHz superconducting part with geometric beta factor of 0.61 (LB650) that
encloses 36 five-cell elliptical cavities in 9 cryomodules,
accelerating beam from 177 MeV to 516 MeV.
Target cavity accelerating gradient is set at 16.9 MV/mwith a quality factor higher than 2.4 1010, an unprecedented
working point for this type of resonators [2].
The complete series of 38 SC cavities (36 plus 2 spares)
will be handed over to the project once qualified throughcold vertical test and they will be in a ready-for-string-assembly configuration: jacketed, fully dressed and undervacuum.

cavity in its final configuration upon delivery to string assembly site is instead shown in Fig. 1.
Table 1: Design Parameters of LB650 Cavity
Parameter
βgeometricFrequency
Number of cells
Iris diameter
Cell-to-cell coupling, kcc
Frequency separation π-4π/5
Eq. diameter - IC
Eq. diameter - EC
Wall angle – Inner-End cells
Effective length (10*Lhc)
Optimum beta βopt
Epeak/Eacc @ βopt
Bpeak/Eacc @ βopt
R/Q @ βopt
G @ βopt
Stiffening ring radius
Wall thickness – discs
Longitudinal stiffnessLong. frequency sensitivity
LFD coefficient- kext at 40 kN/mm Pressure sensitivity- kext at 40 kN/mm -

Value
0.61
650 MHz5
88 mm
0.95 %
0.57 MHz389.8 mm
392.1 mm
2°704 mm
0.65
2.40
4.48 mT/(MV/m)
340 Ω
193 Ω
90 mm
4.5 mm
1.8 kN/mm
250 kHz/mm-1.4 Hz/(MV/m)

2-11 Hz/mbar

THE PIP-II LB650 CAVITYINFN LASA provided the electromagnetic and mechanical design for the LB650 resonator, fully compatible to theperformances and technical interfaces posed by the project
as well with beam pipes and flanges, power coupler, heliumtank, tuner.
Key design parameters and target performances of the
INFN designed LB650 resonator are shown in Table 1, the
TUPB074476

Figure 1: LB650 cavity.
Following the valuable know-how available in the PIPII community and the preliminary R&D done and being
done (described later in this paper and in more details in[3]), the target surface processing cycle for LB650 has been
defined as:
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ADVANCED ALGORITHMS FOR LINEAR ACCELERATOR DESIGNAND OPERATION
Y. K. Ong∗ 1 , L. Bellan, A. Pisent, M. Comunian, E. Fagotti, D. Bortolato, M. Montis,
M. Giacchini, O. Carletto, INFN-LNL, Legnaro, Italy1also at La Sapienza University of Rome, Italy
THE ANTHEM MEBT LINE

Abstract
In this paper, we investigate the usage of advanced algorithms, specifically Bayesian optimization, adapted for
optimizing the design and operation of different linear accelerators (LINACs). The aim is to enhance the design
efficiency and operational reliability and adaptability of linear accelerators. Through simulations and case studies, wedemonstrate the effectiveness and practical implications ofthese algorithms for optimizing LINAC performances acrossdiverse applications.

INTRODUCTION
The field of accelerator physics has advanced significantly,
driven by the demand for higher performance in particle
accelerators used in research, medical, and industrial applications. Conventional methods for designing and operatingthese complex systems, such as Nelder-Mead Simplex [1]and robust conjugate direction search [2], often rely on extensive simulations and expert knowledge due to the large andvaried accelerator components and parameters needed to be
tuned. Therefore, developing more efficient ways to solve
complex optimization problems through advanced machinelearning (ML) based algorithms are being explored.
Among the advanced algorithms, Bayesian Optimization(BO) has been gaining popularity within the accelerator community for both offline and online tuning due to its flexibility,
low initialization effort, fast convergence, and robustness tonoisy environments [3–5]. BO builds a probabilistic surrogate model, typically a Gaussian process [6], of the objectivefunction. This model predicts the function’s behavior andquantifies uncertainty. The optimization process iteratively
selects new evaluation points based on this model, balancing
exploration of the search space with exploitation of known
high-performing regions. An acquisition function guides
the selection of points by considering both predicted performance and uncertainty. This efficient approach finds optimal
parameters with a limited number of evaluations.
In this paper, we explore the application of Bayesian Optimization in the design of the ANTHEM MEBT line and theoperation of the TAP accelerator complex at INFN-LNL. We
discuss the challenges in accelerator optimization, review
current techniques, and present case studies demonstrating
the effectiveness of Bayesian optimization.
∗ ysaong@lnl.infn.it

TUPB075
480

The AdvaNced Technologies for Human-centrEd
Medicine (ANTHEM) project aims to develop technologies
for the healthcare of chronic patients. One of its main
proposals is the construction of an Accelerator-based
Boron Neutron Capture Therapy (A-BNCT) facility in
Caserta, Campania, Italy. This facility will utilize ahigh-intensity proton source with the TRASCO RFQ as the
proton accelerator, operating at a frequency of 352 MHz
and an output beam energy of 5 MeV at a 30 mA beam
current [7]. The medium energy beam transport (MEBT)
line, located after the RFQ, is responsible for transportingand manipulating the spatial distribution of the beam tothe target for optimal neutron production. As presented inFig. 1, the MEBT line design includes various magnetic
elements, such as quadrupoles, a dipole, and a pair ofoctupoles, which utilize the tail folding technique to achievea uniform beam distribution at the target [8]. Good beam
uniformity at the target with an area of 120 × 120 mm2
is necessary to maintain the beam power deposition ataround 1 kW/cm2 for optimal neutron production and target
operation.

Figure 1: ANTHEM MEBT line beam envelopes withquadrupoles, dipole and octupoles being the blue, red, andpurple elements respectively. Blue line: x. Red line: y.

Bayesian Optimization for Shaping the Beam Uniformity at the Target
The manipulation of the beam distribution is performed
through the activation and optimization of the octupole
strengths and the addition of a collimator. However, before proceeding with this step, the MEBT line was first optimized to transport the beam without losses to the target
using TraceWin, a tracking program that utilizes a PIC technique to calculate the beam dynamics and exploit the spacecharge-induced behavior of the beam [9]. Additionally, the
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BEAM TRANSIENT STUDIES FOR THE JAEA-ADS LEBT
B. Yee-Rendon∗ , Y. Kondo, J. Tamura, F. Maekawa, S. Meigo
Japan Atomic Energy Agency (JAEA), Tokai, Japan
Abstract
The Japan Atomic Energy Agency (JAEA) is designinga 30-MW CW proton linear accelerator (linac) for nuclear
waste transmutation. Space-charge is the primary challengein achieving low losses and high beam quality for high-power
accelerators, especially at low energy levels where spacecharge forces are greater. To counteract the space-charge
effects, the low-energy beam transport (LEBT) uses a magnetostatic design to enable the neutralization of the beam
charge, the so-called space charge compensation. The neutralization is an accumulation process that reaches a chargebalance between the main beam and the opposite ionized particles. However, this equilibrium is destroyed by the chopper
system used during beam ramping. During those transient
regimes, the beam optics conditions are not optimal for thebeam, producing considerable degradation that can end inserious damage to the accelerator. Thus, analysis of beam
behavior at these periods is essential to develop a robust
design and an efficient operation of the JAEA-ADS linac.
This study presents the beam dynamics of neutralizationbuild-up and chopper operation for the JAEA-ADS LEBT.

INTRODUCTION
The Japan Atomic Energy Agency (JAEA) is designingan accelerator-driven subcritical system (ADS) for nuclear
waste transmutation [1]. To this end, JAEA will use a30-MW continuous-wave superconducting proton linear accelerator [2]. As with any high-intensity accelerator, spacecharge is the main challenge to avoid beam losses. Therefore, the low-energy beam transport (LEBT) uses a spacecharge compensation (SCC) design [3] to transport the beamfrom the ion source to the RFQ to avoid large emittance
growth caused by space-charge effects. SCC occurs whenthe main beam ionizes the residual gas, producing secondary
particles. These secondary particles with an opposite charge
regarding the main beam are trapped in the beam potential
and accumulate until reaching a steady equilibrium state.
This leads to a screening of the space charge forces.

Figure 1: Schematic view of the JAEA-ADS LEBT design.
Figure 1 and Table 1 show the LEBT design and its main
parameters, respectively. In this design, the chopper is∗ byee@post.j-parc.jp

TUPB076484

placed between the solenoids, bringing solenoid 2 closer
to RFQ to achieve a more convergent beam.
Table 1: Main Parameters for the JAEA-ADS LEBTParameter
Particle
Beam current (mA)
Beam energy (keV)
Solenoid length (mm)Solenoid 1 position (mm)Solenoid 2 position (mm)Chopper length (mm)Chopper position (mm)Length (mm)Proton
25
35
300
500
1680
125
1347.51960

Previous LEBT model [4] considered a piecewise constant space-charge compensation. However, experiments
and studies show a more complex profile [3, 5]. Thus, thiswork improves the accuracy of SCC by developing a timedependent LEBT model utilizing Warp [6] to include theionization process. Furthermore, beam transient analysis
will be utilized to determine the beam structure for nominal
operation by taking into account the conditions needed toreach a steady state and the beam power ramp strategies byinvestigating the chopper effects.

BEAM TRANSIENT STUDIESTransient beam studies were conducted using Warp, a 3Dparticle-in-cell program developed at Lawrence Berkeley
National Laboratory to model high-intensity beams [7–9].
Warp is a self-consistent code, which means it can accurately
simulate space charge effects in the beams.
In SCC studies, the SCC level (𝜂) is a standard figureof merit used to evaluate the reduction in the effect of thecurrent space charge. 𝜂 is quantified as [10]:# negative particles,(1)# positive particles
where # of charged particles that are contained to a certain
root-means square (rms) beam size.
Another important variable is the SCC transient time(𝜏scc ), which provides information about the time required
for a particle of the beam to produce a neutralizing particle
in the residual gas. 𝜏scc is defined as [3, 5]:
𝜂=1−

𝜏scc =

𝑘𝑇,
𝜎gas 𝑃𝑣𝑏(2)

where 𝜎gas is the cross-section of the beam particle to theresidual gas, 𝑘 is the Boltzmann constant, 𝑇 is the temperaTUPB: Tuesday Poster Session
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THE LINACS SIMULATION FRAMEWORK
B. Yee-Rendon∗ , Japan Atomic Energy Agency (JAEA), Tokai, Japan
R. A. Jameson, Goethe Universität, Frankfurt, Germany
M. Okamura, Brookhaven National Laboratory, Upton, NY, USA
C. Li, Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
P. Jiang, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China
J. M. Maus, NTG Neue Technologien GmbH und Co KG, Gelnhausen, Germany
Abstract
LINACS is a simulation framework for designing, simulating, and analyzing optics and beam dynamics of charged
particles in particle accelerators. LINACS is an opensource software that enables the user complete control overall design and simulation parameters of RFQs. This includes beam-driven design, fully 3D simulation using precise quadrupolar symmetry, and rigorous Poisson solution
for external and space charge fields. The code can handle
simultaneous particle beams with analytical input distributions and allows input beam scans. The software offers a
relatively short running time and provides extensive analysis techniques. This work provides a historical overview of
the code, presents results from RFQ models, and discusses
future developments.

INTRODUCTION
Systematic design code for linear accelerators altogether
is rare, and comprehensive frameworks that include spacecharge physics as a primary focus and utilize an inside out
design, i.e., a design that specifies the desired beam behavior
as influenced by space charge and specifies the external fieldthat produces that behavior, are currently only represented
by LINACS [1]. As a result, the emphasis is heavily placedon design aided and followed by simulation, both of which
require equal care and a framework approach. The exampleof RFQ design is used to illustrate this point, as it is considered the most challenging linac to design due to the beam’s
evolution from DC injection to the formation of accelerated
bunches.
R. A. Jameson and several students at the Institut für Angewandte Physik (IAP) aimed to enhance the physics fidelityof general linacs, specifically focusing on RFQ design, simulation, and optimization [2].
The motivations included:• Full and direct control over all parameters.
• Close the agreement between actual RFQ performanceand simulations.
• Improving the physics modeling.
• Open source programs.
• Develop guidelines for model optimization.
The ultimate objective was to develop a new, open-sourcecode called LINACS for particle accelerator design andsimulation. This code would integrate the most advanced∗ byee@post.j-parc.jp

TUPB077
488

physics that current computer technology can accommodate.
It would also provide options for the designer to prioritize
between accuracy and execution speed, with a clear understanding of the potential consequences. Additionally, thecode would offer a versatile library of analysis capabilities.

LINACS FRAMEWORKThe LINACS framework is composed of three main codes:
LINACSrfqDES, LINACSrfqSIM, and LINACSapf. The
first two are specialized for RFQ design, and the last one
was developed for the Alternating-Phase-Focused (APF)
linacs [3]. In this report, we will focus on the RFQ codes:
LINACSrfqDES and LINACSrfqSIM.
The LINACSrfqDES framework controls all RFQ parameters, including the space charge physics. This ensures that thebeam is controlled in the design by requiring the root-meansquare (rms) beam envelope to be matched transversely andlongitudinally at each cell. Therefore, the rms beam envelope is known at each cell. LINACSrfqDES is unique inusing a good approximation of the external field (8-term
multipole), applied in the design at the rms beam sizes, sothat the design and LINACSrfqSIM are fully connected.

Figure 1: Graphical user interface for the RFQ design.
Figure 1 shows the graphical user interface for the RFQ
design. Using this interface, the user can define the generalparameters of the RFQ, shaper, and main RFQ parameters.
The user has the option to choose from various predefinedrules, or they can create and implement their own rules tocontrol the parameters. The simul bottom on the top-right
TUPB: Tuesday Poster Session
MC3.5 RFQs

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PROGRESS OF THE SPOKE CAVITY PROTOTYPINGFOR THE JAEA-ADS LINAC
J. Tamura∗ , Y. Kondo, B. Yee-Rendon, S. Meigo, F. Maekawa, JAEA/J-PARC, Ibaraki, Japan
E. Kako, K. Umemori, H. Sakai, T. Dohmae, KEK/iCASA, Ibaraki, Japan
Abstract
The Japan Atomic Energy Agency (JAEA) has been
proposing an accelerator-driven nuclear transmutation system (ADS) as a future nuclear system. Toward the practicaldesign of the CW proton linac for the JAEA-ADS, we are
currently prototyping a low-𝛽 (≈ 0.2) single-spoke cavity.
The cavity fabrication began in 2020. Most of the cavity
parts were shaped in fiscal year 2020 by press-forming andmachining. In 2021, we started welding the shaped cavity
parts together. Each cavity part was welded together by preliminarily examining the optimum welding conditions using
mock-up test pieces. So far, we have fabricated the bodysection and the two lid sections, and have confirmed that
there were no significant problems with the cavity fabricationaccording to the frequency measurement of the temporarilyassembled prototype cavity.

INTRODUCTION
JAEA has been proposing an ADS as a future nuclear system to efficiently reduce high-level radioactive waste generated in nuclear power plants. In the ADS, long-lived nuclides
are transmuted to short-lived or stable ones. One of the challenging R&D subjects to realize the ADS is the reliabilityof the accelerator [1, 2]. In the JAEA-ADS, a high-power(30 MW) proton beam with a final energy of 1.5 GeV isrequired with high reliability. Because the accelerator needs
to be operated in CW mode, a super-conducting (SC) linac
would be a suitable solution. The latest design of the JAEAADS linac is reported in Refs. [3, 4]. As shown in Fig. 1,
the proposed linac consists of a normal-conducting radiofrequency quadruple (RFQ), half-wave resonator (HWR),
low-𝛽 and high-𝛽 single-spoke resonators (SSR1 and SSR2,
respectively), and low-𝛽 and high-𝛽 elliptical cavities (ELL1and ELL2, respectively).

Figure 1: Proposed acceleration structure of the JAEA-ADS
linac.

As a first step toward the practical design of the JAEAADS linac, we have decided to prototype the low-𝛽 singlespoke cavity and conduct a high-field performance test of
the prototype spoke cavity at liquid helium temperature.
The spoke cavity prototyping will provide us with various

insights on the development of SC cavities with TEM 𝜆/2mode resonance. In addition, the high-field cavity testing
will provide valuable information such as how much field
gradient can be achieved with reasonable stability. Therefore,both prototyping and performance testing are essential toensure the feasibility of the JAEA-ADS linac. In this paper,
the progress of the spoke cavity prototyping for the JAEAADS linac is presented.

CAVITY DESIGN
The prototype spoke cavity with an operating frequencyof 324 MHz was designed by electromagnetic simulation [5],and its dimensional parameters were optimized for higher
cavity performance [6–8]. The cross-sectional views of thedesigned cavity are shown in Fig. 2. The cavity’s design
parameters are listed in Table 1. The multipactor analysis of
the designed cavity without the coupler ports was presented
in Ref. [7].

Figure 2: Cross-sectional views of the designed cavity.

Table 1: Design Parameters of the Prototype Spoke Cavity
Parameter
𝑓0
𝛽g
𝛽opt
Beam aperture
Cavity diameter
Cavity length
𝐿 eff = 𝛽opt 𝜆𝐺 = 𝑄 0 𝑅s
𝑇 (𝛽opt ) = 𝑉acc /𝑉0
2 /𝜔𝑊
𝑟/𝑄 = 𝑉acc
𝐸 peak /𝐸 acc
𝐵peak /𝐸 acc

Value
324 MHz
0.188
0.24
40 mm
∼500 mm
300 mm
222 mm
90 Ω
0.81
240 Ω
4.1
7.1 mT/(MV/m)∗ jtamura@post.j-parc.jp

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MC3.7 Superconducting structures32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB081

H.-S Kim*, S.-H. Moon, D.-H. Kim, S. Lee, H.-J Kwon, Korea Multipurpose Accelerator Complex,
Korea Atomic Energy Research Institute, Gyeongju, Korea
Abstract
Since the second half of 2013, the Korea Multi-purpose
Accelerator Complex (KOMAC) has been supporting user
beam services with a 100 MeV proton linac. Given that the
proton accelerator has been in operation for over 10 years
and its cumulative operating time has surpassed
33,000 hours, we believe it is an opportune moment to establish a long-term plan to address the aging of the accelerator. To replace the current RFQ, which is experiencing
performance degradation (particularly in reduced beamtransmission), we have designed a new RFQ with several
modifications. We eliminated the resonant coupling structure located in the middle of the old RFQ to simplify thedesign and facilitate tuning. Additionally, we increased the
RFQ length from 3,266 mm to 3,537 mm to improve beamtransmission efficiency in high-current mode. An error
study on the new structure has shown that the design is robust against various error sources. The details of the RFQ
design, along with the fabrication status, will be presented.

INTRODUCTION
The RFQ at the Korea Multi-purpose Accelerator Complex (KOMAC) was designed to accelerate a proton beamfrom 50 keV to 3 MeV.

Figure 1: Existing RFQ at KOMAC.

Consequently, we have decided to design a new RFQ toreplace the existing one.

DESIGN OF NEW RFQ
The new RFQ incorporates several improvements andmodifications but remains quite similar to the existing RFQ.
Therefore, the new RFQ parameters, as shown in Table 1,
are also similar to those of the existing RFQ.
Table 1: Parameters for New RFQ
Parameter

Value

Input beam energy

50 keV

Output beam energy

3 MeV

Operating frequency

350 MHz

Transverse emittance

0.2 π. mm. mrad

Longitudinal emittance

0.107 deg.MeV

RFQ type

4 - vane

Vane voltage

85 kV

ρ/r0

0.87

Length353 cmWhile many parameters remain the same, a majorchange in the new RFQ is the adjustment in the energy
range of the gentle buncher. In the old RFQ, the energy
range of the gentle buncher varied from 86.5 keV to
550 keV, whereas in the new RFQ, it ranges from 86.5 keV
to 580 keV. Although this difference is only 30 keV, wefound that extending the energy range improves beamtransmission rates.

Figure 1 shows the existing RFQ at KOMAC. This RFQ
was successfully commissioned and has been in operation
for approximately 20 years since its initial commissioningin 2004 [1-2]. However, the performance of the RFQ has
gradually degraded over time.

Figure 2: Observed vane electrode damage.
We suspect that the degradation in performance is due todamage to the RFQ vanes, which was confirmed throughdirect observation using an endoscope. We observed numerous arcing spots and surface degradation (Fig. 2).
TUPB: Tuesday Poster Session
MC3.5 RFQs

Figure 3: Beam transmission rate with various cases.
The Fig. 3 illustrates the beam transmission rate acrossdifferent scenarios. Mod 1 represents the existing RFQ,
while M1 is similar to Mod 1 but without the focusing
TUPB081495

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NEW 3-MeV RFQ DESIGN AND FABRICATION FOR KOMAC

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EVALUATING BEAM NEUTRALIZATION AND TRANSPORT DYNAMICS
IN LASER-DRIVEN ION ACCELERATORS
H. Matsumoto†, 1, H. Sakaki1, Y. Watanabe, Kyushu Univ., Fukuoka, Japan
T. Endo, M. Hata, K. Kondo, K. Nagashima, QST, Kyoto, Japan1
also at QST, Kyoto, Japan
Abstract
Laser-driven ion acceleration [1, 2] produces a high ion
density at the source point, with a source diameter of lessthan one millimeter, and a bunch length of less than a few
picoseconds. Typically, such a low-energy, high-density
beam with short inter-ion distances causes explosive spacecharge forces in the longitudinal and transverse directions,leading to significant emittance growth. However, thetransverse emittance observed in the beam a few centimeters downstream of the source point is an order of overmagnitude better than that of a typical RF accelerator beam
[3,4]. This is the because the accelerated ion beam is transported in a state like "plasma: the charge neutralized" bymoving electrons, but it has not been studied in detail using
particle transport simulations. To understand the beamtransport dynamics, we diagnose the space charge neutralized beam by developing a novel PIC code that continuously and seamlessly simulates the laser-driven ion acceleration from the source to the beam measurement point.

LASER-DRIVEN ION ACCELERATION
Ion Acceleration Mechanism
Laser-driven ion acceleration is a method of producing
MeV energy ions by irradiating a thin film target (thickness< µm) with a high intensity laser (> 1018 W/cm2). The ion
acceleration process, Target Normal Sheath Acceleration(TNSA) [5], is shown in Fig. 1.

3. The detached electrons are trapped in the ion’s electricfield. As a result, a very strong electric field (~ TV/m)is generated between ions and electrons.
4. Ions are accelerated to MeV class by generated electric field.
Thus, the TNSA process with a short-pulse laser is a micro-scale ion acceleration process, where the source diameter is less than one millimeter, and the beam direction isless than a few picoseconds at the source point.

Space Charge Neutralization
At the source, low energy and high instantaneous current
ion beams are not efficiently transported downstream dueto the explosive force created by space charge effects between ions. In the TNSA process, however, both electrons
and ions are accelerated in the same direction, resulting in
the creation of a plasma beam with charge neutralization,
where both ions and electrons share the same velocity vector. The space charge force of the ion beam from the TNSA
process is cancelled out by the effect of charge neutralization, a low transverse emittance is observed in the actual
ion beam. Considering applications with the TNSA process
ion beam, it is necessary to design an optimal beamtransport system to maintain the low emittance. It can beinferred that emittance growth is caused when transient comoving electrons are removed from the beam, such as
when passing through a magnetic field in the first optics.
To design the optimal transport of this low emittancebeam, a space charge simulation code is required that continuously and seamlessly calculates both the TNSA process(micro-domain: ~µm, ~ps) and the beam transport part
(macro-domain: ~m, ~µs).

PARTICLE-IN-CELL SIMULATION

Figure 1: The mechanism of laser-driven ion acceleration.
The TNSA process is,
1. Focused high intensity laser interacts on a thin film
target, and the target ionized by the electric field of thelaser.
2. Produced ions and electrons are subjected to a ponderomotive force in the target normal direction. The
electrons receive energy and detach from the target.

To understand the particle physics of TNSA beamtransport, it is necessary to continuously simulate the ion
and electron distribution from micro-domain to the macrodomain. In general, during macro-domain beam transport
simulations, the beam is treated as a macroscopic group,
and its space-charge effects are simply modelled as a linear
effect to reduce computational resources. However, themodel cannot simulate in detail the nonlinear emittance
growth in TNSA beam transport, where the micro-domain
space-charge effects between ions and electrons are constantly changing. To solve this problem, it is necessary tocontinuously and seamlessly simulate the ion distribution
in the micro-domain and the macro-domain, a Start-to-End
simulation, we are trying to develop a novel simulation using the particle-in-cell method.

____________________________________________† email address: Matsumoto.haruya.876@s.kyushu-u.ac.jp
TUPB087
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ANALYSIS OF REDUNDANCY DESIGN AND RELIABILITY ESTIMATION
OF 60 kW CW RF HPA FOR ALS-U PROJECT AT LBNL
S. Basak†, B. Flugstad, D. Nett, K. Baptiste, LBNL, Berkeley, CA, USA
R. Kobana, K. Hirano, T. Sueishi, S. Hihara, R&K Company Ltd, Fuji City, Japan
Abstract
The two units of 60 kW CW AR RF High Power Amplifier (HPA) are critical major equipment in new RF system
for ALS-U project at LBNL and so it has been designed
and built with a modular redundant topology having large
array of 96 RF final PA modules (each delivering ~ 700 W
RF output) that are combined in parallel, and large 30 DC
PS modules (each ~ 5 kW DC power) operating in parallel
for achieving very high reliability (MTBF ~ 135,000
hours) and availability (~ 99.997%) of RF HPA which isessential for continuous 24/7 beam operation. The redundancy design to modules failures is such that in the eventup to 10% failures of RF PA modules and/or up to 15%
failures of DC PS modules the HPA still can generate minimum 48 kW CW RF output that is needed for full beam
power and so RF power headroom of 12 kW is built in. The
operating power levels and temperatures of all components
in HPA are well below to their maximum ratings for highreliability. The MBTF values of subsystems in HPA has
been estimated based on components with high failures
rates. The reliability probabilities having exponential distribution parameterized on failure rate were determined
and the binomial distribution used for modules having redundancy. This paper presents such redundancy design
analysis of HPA to such modules failures to achieve suchminimum output power. Also, the Availability (~99.997%)
and the Reliability (MTBF ~ 135,000 hours) Estimation
analysis of the overall HPA with such redundancy to modules failures is presented.

as to generate the required 500 kV cavity voltage to deliver
energy to the circulating electron beam in AR.
The solid-state based RF HPA is a complex piece ofequipment that is the preferred topology in most Laboratories for new projects and for replacing earlier obsolete
tube-based RF amplifiers because of known benefits likegraceful degradation, no high voltages, high efficiency,
modularity, high MTBF, and low phase noise.
The design and construction features of various subsystems in the AR RF HPA viz., AC, DC, PA modules, combiner, LCW cooling, controls, etc. has been described inRef. [1]. The HPA has been designed and manufactured
thorough a joint effort of engineers from LBNL and engineers at vendor R&K Company Ltd., Japan and a pictureof the HPA taken during the factory acceptances test is
shown in Fig. 1.

INTRODUCTION
The ALS-U project at LBNL is aimed to create a worldclass facility to provide users with bright, high-coherentflux soft x-rays that are unmatched in the world now. The
ALS-U project will provide an increase in brightness andcoherent flux of soft x-rays (at1 keV) of at least two ordersof magnitude beyond today’s ALS capabilities. It will also
provide infrared and hard x-ray capabilities comparable tothe present-day ALS. There will be an upgraded Storage
Ring (SR) optimized for low emittance, high soft x-ray
brightness and coherent flux and a new Accumulator Ring
(AR) for full-energy swap-out injection and recovery of
beam bunch trains. The new AR RF system is comprisedof two independent AR RF accelerating cavity subsystems,
each having a low-level RF controller, an RF HPA, highpower circulator, high power RF switch, rigid coaxial
transmission lines, and ancillary support equipment. EachAR RF HPA will provide the requisite controlled, stablehigh-power RF to each normal conducting RF cavities so___________________________________________†ssbasak@lbl.gov
TUPB089
502

Figure 1: Photo of the AR RF HPA taken during FAT.

HPA MAIN SPECIFICATIONSThe HPA main specifications are tabulated in Table l.
Table 1: HPA Main Specifications
Specification
Center Frequency
1dB BW
1dB Output Power
Input Power
Wall plug Efficiency
Group Delay
Spurious
Stability (long term)

Value
500.394 MHz≥ 5 MHz≥ 60 kW CW≤ 0 dBm≥ 55 %≤ 200 ns
≤ -80 dBc
≤ ± 0.5 dB ; ≤ 10°
TUPB: Tuesday Poster Session

MC4.6 RF power sources and power couplers

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB090

C. Mitchell† , A. Huebl, M. Garten, R. Sandberg, R. Lehe, A. Formenti, J. Qiang, and J-L. Vay
Lawrence Berkeley National Laboratory, Berkeley, CA, USA
Abstract
The code ImpactX represents the next generation of theparticle-in-cell code IMPACT-Z, featuring s-based symplectic tracking with 3D space charge, parallelism with GPU acceleration, adaptive mesh-refinement, modernized language
features, and automated testing. While the code contains
features that support the modeling of both linear and circular accelerators, we describe recent code development
relevant to the modeling of high-intensity linacs (such as
beam transport for the Fermilab PIP-II upgrade), with a focus on space charge benchmarking and the impact of novel
code capabilities such as mesh refinement.

BACKGROUND
High-intensity proton and ion linacs are critical to meetthe needs of future colliders, spallation neutron sources, andneutrino sources. Accurate beam modeling requires highspatial resolution and particle statistics, with the ability toresolve low-density beam halo and particle loss. To enable
integrated start-to-end modeling with reasonable computing
times, to enable large ensembles of simulation runs for optimization and for training of machine learning (ML) models,
and to prepare for future Exascale computing systems, existing software must be modernized to take advantage ofstate-of-the-art computer hardware, including GPUs. The
Beam pLasma & Accelerator Simulation Toolkit (BLAST)
is an open ecosystem of codes, that can be combined witheach other and with machine learning frameworks to enable
integrated start-to-end simulation of accelerator beamlines
for accelerator design [1]. Examples of BLAST tools include
the PIC codes WarpX and ImpactX.

IMPACTX FEATURES
ImpactX [2,3] is a GPU-capable C++ successor to the Fortran code IMPACT-Z [4, 5], built on the AMReX software
framework [6], for modeling relativistic charged particle
beams in linacs or rings. Similar to IMPACT-Z, tracking
is performed with respect to the path length variable 𝑠, andspace charge is included using a second order operator splitting [4]. All tracking methods are symplectic by design,and maps are used where possible for efficient particle pushing. By default, the 3D space-charge fields are computedwith an iterative Multi-Level Multi-Grid (MLMG) Poissonsolver [6], providing support for adaptive mesh refinement.
The code provides support for commonly-used elements(drifts, quads, solenoids, dipoles, multipoles, and cavities),∗ Work supported by U.S. Department of Energy, Office of Science, Officeof High Energy Physics† ChadMitchell@lbl.gov

TUPB: Tuesday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

as well as some specialized elements (plasma lens models,
IOTA nonlinear elliptic magnet). Exact nonlinear maps
are implemented for several elements (sector bends, drifts,
uniform electrostatic gaps, and thin multipoles). The codeis fully open to the community, and it is integrated into
the BLAST software stack for interoperability with other
BLAST codes.

Capabilities Added in SciDAC
ImpactX originated in an LBNL-supported LDRD as acode supporting magnetic lattice elements and high resolution space charge. As part of an ongoing HEP SciDAC-5
project [7, 8], the code has undergone active development
to facilitate the modeling of high intensity linacs, as partof a collaborative effort with FNAL to develop a “virtual
test stand” of the PIP-II accelerator complex (Fig. 1) [9].
Capabilities added include:

Figure 1: The Fermilab accelerator complex in preparation
for the PIP-II upgrade. H− ions are accelerated to 800 MeV
in the superconducting PIP-II linac and injected into the
Booster synchrotron. From there they are delivered to further
accelerators and experiments.
• user control of mesh refinement (for MLMG solver)• a 3D IGF Poisson solver with open boundaries [10]• RF cavity models - using on-axis electric field data
• openPMD standardized format for particle output [11]• elliptical and rectangular transverse apertures• lost particle phase space diagnostics• support for rotation and misalignment errors• soft-edge magnet fringe field models (quads, solenoids)
Additional relevant tools include Python scripts for postprocessing (e.g., Twiss optics, beam visualization) and optimization (e.g., matching).
TUPB090505

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IMPACTX SPACE CHARGE MODELING OF HIGH INTENSITY LINACSWITH MESH REFINEMENT∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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G. Kazakevich†, R.P. Johnson, Muons, Inc., Newport News, VA, USA
T. Khabiboulline, V. Yakovlev, Fermilab, Batavia, IL, USA
Yu. Eidelman, Eidelman Scientific Consulting, Naperville, IL, USA
Abstract
Modern CW or pulsed Superconducting RF (SRF)
accelerators require efficient RF sources controllable inphase and power with a reduced cost. Therefore,
utilization of the high-power CW magnetrons as RF
sources in SRF accelerator projects was proposed in a
number of works, e.g., [1, 2]. But typically, the CW
magnetrons are designed as RF sources for industrial
heating, and the lifetime of the tubes is not the firstpriority as it is required for high-energy accelerators. The
high-power industrial CW magnetrons use the cathodes
made of pure tungsten. The emission properties of thetungsten cathodes are not deteriorated much by electron
and ion bombardments, but the latter causes sputtering of
the cathode in the magnetron crossed fields. The
sputtered cathode material covers the magnetron interior.
That leads to sparks and discharges limiting magnetrons
lifetime. We considered an analysis of magnetron failuremodes vs. output power [3]. We developed a model ofionization of the residual gas in the magnetronsinteraction space and simulated the spattering of thecathode in 100 kW CW magnetrons to estimate the life
expectancy. Basing on results we proposed ways toincrease the CW magnetrons longevity for SRF
accelerators.

INTRODUCTION
Our consideration is based on analysis of initiallydeveloped by Burley Industries Inc. CW, 915 MHz, highpower, 10 vanes magnetrons with strapped resonant
system vs. failures at power levels of 30, 50 and 75 kW[3] and analysis of impact of ionization of the residual
gas in vicinity of the cathode. As it was shown in ref. [3]for 30 kW CW magnetrons with anode voltage of 12.6
kV and anode current of 2.8 A and the cathode filament
power of 1.14 kW the average time in the field for new
30 kW tubes was 119 months, i.e., ~20∙103 hours. For 50
kW tubes at the anode voltage of 15 kV, anode current of
4 A at the filament cathode power of 0.95 kW andincreased magnetic field it was ~5∙103 hours. The
majority of failures of these tubes were caused byinternal arcing. For 75 kW tubes at the anode voltage of
17.5 kV at the anode current of 5.1 A at the cathodefilament power of 1.54 kW and additionally increased
magnetic field the life time was less. In Ref. [3] was* Supported by scientific collaboration of Muona, Inc. and Fermi
National Accelerator Laboratory, Fermi Research Alliance, LLC
under.CRADA-FRA-2017-0026.
† e-mail: gkazakevitch@yahoo.com; grigory@muonsinc.com

TUPB: Tuesday Poster Session
MC4.6 RF power sources and power couplers

noted that the internal arcing was considerably greater intubes output power of 60 kW and more. Thus, an increaseof the CW magnetrons anode voltage and current reduces
the tubes life time because of internal arcing. We
consider here the reasons of this.

IONIZATION OF THE RESIDUAL GAS IN
A CW HIGH-POWER MAGNETRON
We consider impact of motion of electrons at operationof high-power CW magnetrons on the tubes life time witha simple model of ionization of the residual gas in amagnetron interaction space. Typical current density oftungsten cathodes is about 0.3 A/cm2 [4]. This requires
the cathode temperature of about 2500 K. An operation of
the cathode at such high temperature and the cathodeadditional overheat caused by electron back-stream
worsen the vacuum in the cathode vicinity approximately
by an order of magnitude. If in a cold magnetron thevacuum pressure is typically ≤10-6 torr, during the tube
operation the average vacuum pressure in the interaction
space is increased to ~5∙10-6 torr or more.
In the interaction space of operating magnetron,
Larmor electrons move along trochoids during few
cyclotron periods alternately approaching the cathode andanode. For 100 kW industrial, e.g., type CWM-100 kW
magnetron, operating at the magnetic field of 0.238 T the
anode voltage is ≈22 kV [4]. At these parameters, theelectron energy on the cyclotron orbits (closer to thecathode) is varied from approximately 0 to 10 keV foreach trochoid period. The radius of the cyclotron orbit is≈0.21 cm.
The ionization cross section of residual gases forenergies of ~100 eV and higher is decreased approximately inversely proportional to the energy of electrons[5, 6]. Then in the estimates one can assume that inionization of the residual gas contribute generally the
Larmor electrons moving along the parts of orbits closer
to cathode. It can be assumed that over several cyclotron
periods the path length of the ionizing electron is of theorder of the length of the Larmor orbit. Compared tohigh-power klystrons the smaller energy of the ionizing
electrons in magnetrons results in much higher
probability of ionization of residual gas by a single
electron. Moreover, the modern klystrons operate atmuch lower pressure of the residual gas due to built-in
ion pumps significantly decreasing the residual gas
pressure. The ionization results in an appearance of
positive ions accelerated towards the cathode. Theirenergy is determined by the average static electric field.
In the industrial CWM-100L magnetron the ion energy is
TUPB091
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ON THE LIFE EXPECTANCE OF HIGH-POWER CW MAGNETRONS FORSRF ACCELERATORS*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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DEVELOPMENT OF PHASE LOCKED OSCILLATOR FEL
FOR HIGH REPETITION MID-INFRARED FREQUENCY COMBS
Y. Sumitomo, T. Kubota, K. Harada, L. Soga, T. Sakai, Y. Hayakawa
College of Science and Technology, Nihon University, Tokyo and Chiba, Japan
Abstract
The mid-Infrared region (2–5 µm) is currently a frontierof laser science with short durations, where many molecular absorbing spectrums exist. The oscillator free electron
lasers have advantages against solid-state laser systems, that
include the fundamental generations of high-intensity midIR pulses with femto-seconds scale short durations, continuous variations of the central wavelength, and the highrepetitions of pulses due to RF accelerations of electron
bunches. Especially, the coexistence of high-intensities andhigh-repetitions at GHz scales is important for the development of mid-IR frequency combs that may open up a new
direction of molecule non-linear reactions. In this paper,
we report on the importance of phase-locking between FEL
pulses that grow up independently due to shot noises for the
mid-IR frequency combs, and the states of development ofa test stand for the phase-locking system.

INTRODUCTION
We have an oscillator free electron laser (FEL) at Nihon
University that equips the potential generating mid-infraredlaser with a ultra-short duration less than 100 fs. The characteristics of our accelerator includes accelerations up to
100 MeV at 2.856 GHz, by RF macro pulse widths lessthan 20 µs, that enable FEL lasers to persist more than 10 µs
in terms of macro pulse train widths. This persistent FEL
laser is quite helpful to make the micro pulse length shorterbut keeping the pulse energy higher since the FEL pulses
needs enough durations to grow, especially at the perfectsynchronization of FEL cavity against the repetition of electron pulses. In Fig. 1, we illustrate a simulation result under
the perfect synchronization condition [1] using the set of

Figure 1: A simulation example of pulse growth respecting
the oscillator FEL under the perfect synchronization condition [1].
TUPB095
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Figure 2: A schematic showing the relation between highrepetition pulses and comb separations in frequency domain.
parameter assuming our experimental operation. Also forreference, our recent experimental records show the micropulse energy of over 1 µJ persistent among about 10 µs at the
2.856 GHz operations.
The mid-IR region is currently a frontier of laser science
accompanying the recent technology generating ultra short
femto-seconds scale pulses. There are many efforts devoted
to generate so-called frequency combs at the mid-IR, where
many topics of molecular science are related (see for instancea review article [2]). For the generations of frequency combs,
the shorter pulse widths are important to have a frequency
broadening so as to make enough bins in the comb. Also, thehigh-repetition of pulses is related to a power concentrationof each bin in frequency space since the separation of bins
is broadened while the total power is not changed.
We illustrate a schematic describing these relations for abetter understanding in Fig. 2. In the development of solidstate lasers, the high-repetition mid-IR pulses are likely togenerate by non-linear downward conversions from near-IR
lasers where the efficiency of conversions is quite low. The
short resonators are used for generating the high-repetition
pulses over GHz ranges, but the pulse energy decreases dueto the split.
Hence, we consider that the acceleration based generations of mid-IR frequency combs have advantages, for highpower pulse energy by the fundamental oscillator FEL lasers,and for the high-repetitions of pulses due to RF accelerations
at GHz regions. We can also realize the ultra-short pulsesof femto-seconds scale durations and make them shorter by
TUPB: Tuesday Poster Session
MC2.4 FELs

A. Al Marzouk† , Northern Illinois University, DeKalb, IL, USA
P. Piot, Argonne National Laboratory, Lemont, IL, USA
Abstract
Producing bright electron beams is crucial for coherent
light sources, where increasing the peak current is typicallyaccomplished through bunch compression in magnetic chicanes. Alpha magnets, with their unique phase-space manipulation capabilities, have emerged as an attractive choicefor compressing sub-10 MeV electron beams generated byradio frequency photoinjectors. This paper presents detailed
numerical modeling of the beam dynamics of high-charge,
bright bunches undergoing compression within an alphamagnet. The model incorporates space-charge effects andcoherent synchrotron radiation, providing a comprehensive
understanding of the complex interactions and behaviors of
the electron beams during the compression process.

INTRODUCTION
Coherent light sources require bright electron beams withhigh peak currents. To increase the bunch peak current,
longitudinal bunch compression in magnetic chicanes iscommonly employed. This process necessitates an energy
chirp in the electron bunch—a correlation between the particles’ longitudinal positions and their energies—which istypically introduced by RF accelerating structures. Consequently, using chicanes for compression often requires a
relatively large system and is more suitable for high energies(> 10 MeV). For compressing sub-10-MeV beams, a shorterand more compact system is desirable. In this context, alphamagnets combined with RF guns present an attractive andeffective compression scheme for compact injector systems.
Similarly, this class of magnet has been extensively usedin conjunction with thermionic RF guns to generate bunchtrains for injection into storage ring complexes. [1].
An alpha magnet can be assimilated to a half-quadrupole
magnet. In the ideal alpha magnet considered in this paper, a particle injected at an angle of 40.71° to the normalof the magnet entrance exits at the same angle, regardlessof its energy. The particle’s trajectory within the magnet
forms a path resembling the letter alpha (𝛼). Alpha magnets were originally used as achromatic magnetic mirrors
for ion beams [2]. Detailed particle dynamics in the alpha∗ This work was support by the U.S. National Science Foundation underaward PHY-1549132 to Cornell University. This material is partiallybased upon work supported by Laboratory Directed Research and Development (LDRD) funding from Argonne National Laboratory, provided by
the Director, Office of Science, of the U.S. Department of Energy underContract No. DE-AC02-06CH11357. This research used resources of the
National Energy Research Scientific Computing Center; a DOE Officeof Science User Facility supported by the Office of Science of the U.S.
Department of Energy under Contract No. DE-AC02-05CH11231 using
NERSC award BES-ERCAP0020725.
† aalmarzouk1@niu.edu
TUPB0960magnet and its characteristics are described in [3]. Due totheir unique phase-space manipulation capabilities, alphamagnets have garnered significant interest as bunch compression schemes for low-energy electron beams, particularly inapplications like coherent light generation; see, e.g., [4–10].
The particle’s path length inside the alpha magnet varies
depending on its energy such that high energy electrons follow a longer path than that of the lower energy electrons.
Therefore, an energy chirped beam will be compressed after
passing through the alpha magnet similarly to the magnetic
chicane, but with a positive chirp in this case (i.e. highenergy head and low-energy tail). The chirp can be provided
by the RF photoinjector, and hence the compression can be
performed at a low energy right after the gun without theneed for an RF accelerating structure.
At low energies, space charge forces are particularly
strong, especially for higher bunch charges. Additionally,
the bending of electron trajectories through the alpha magnet
causes the emission of synchrotron radiation, which becomes
coherent for short bunch lengths. Therefore, detailed numerical modeling of the beam dynamics for high-charge, brightbunches undergoing compression in an alpha magnet—including space charge effects and coherent synchrotron radiation (CSR)—is essential. Studies on beam dynamics andspace charge simulations are available in Refs. [11–15].
In this paper, we present beam dynamics simulations ofalpha magnet bunch compression using the first-principles,large-scale CSR model, the lw3d code, which naturally
incorporates both space charge and CSR effects. The aim is
to investigate the impact of CSR on beam brightness.

SIMULATION METHOD
The basic approach to CSR involves computing the 3D
electromagnetic radiation fields directly from the LiénardWiechert potentials. The lw3d code, developed byRyne [16], is the only first-principles implementation for 3D
CSR computation. It is a large-scale parallel program that
calculates CSR fields on a 3D grid at each time step. These
fields are then applied to the particles by interpolating themat each particle’s position over time, a method referred to as
the self-consistent mode of lw3d.
An important feature of the lw3d algorithm is its ability
to consider arbitrary external electric and magnetic fields
while most other available CSR codes are limited to dipole
magnets. This feature is essential for the alpha-magnet simulation as we can easily include its fields in the code or import
the field map from a file.
While CSR effects can be mitigated through shielding [17], the current implementation of the lw3d code does
TUPB: Tuesday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

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FIRST-PRINCIPLE BEAM-DYNAMICS SIMULATIONS OF ALPHAMAGNETS FOR BUNCH COMPRESSION OF BRIGHT BEAMS ∗32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB099

S. U. Thielk, R. Agustsson, S. Kutsaev†, A. Pronikov, RadiaBeam LLC, Santa Monica, CA, USA
Abstract
RadiaBeam is fabricating a novel RF vacuum window
for use with the Spallation Neutron Source (SNS) at Oak
Ridge National Laboratory (ORNL). The window featuresa coaxial ceramic window between two waveguides,
brazed as a single assembly. Unlike traditional pillbox window designs, this approach allows the outer diameter of theceramic to decrease and the added benefit of water coolingthe inner diameter of the ceramic. This paper covers theengineering design including details of key features, theimpact of the unique RF design on manufacturability, andmechanical simulations. A status update on the fabricationis also provided with emphasis on the ceramic TiN coating
and brazing process.

coaxial line is more uniform, which reduces dielectriclosses and thermal gradients.

MECHANICAL DESIGN
The engineering design is the culminating result of theRF, thermal, and manufacturability requirements. Withlarge internal volumes and changing cross-sectional geometries, breaking the top-level model into sub-assemblies
and parts required careful consideration for machining,brazing, handling, and cost. The result is a final assemblythat consists of five main sub-assemblies, as demonstrated
in Fig. 1. Each sub-assembly requires multiple braze steps
prior to the final braze using Gold Copper braze alloys.

INTRODUCTION
The radio-frequency (RF) window is a critical aspect ofmost accelerator systems since it is responsible for separating the vacuum volume of the accelerating cavity from the
RF power transmission line. For rectangular waveguide,
this is commonly achieved by brazing a disk of dielectricmaterial, typically alumina, into a cylinder that is thenplaced into the transmission line. Dimensions of the cylinder are optimized to minimize RF reflections often resulting in a diameter for the alumina window that is larger than
the waveguide. For compatibility with the Spallation Neutron Source (SNS), which operates at 300-500 kW average
power and 402.5 MHz, the window transitions from
WR2100 waveguide (533.4 mm x 266.7 mm) on the input
side to half height WR2100 waveguide (533.4 mm x 133.4mm) on the output, or vacuum side of the assembly. The
vacuum side interfaces with the iris coupler for the SNS
drift tube LINAC [1]. A traditional pillbox style window
for this assembly would require a ceramic diameter of approximately 330-360 mm, creating a host of challenges
ranging from ceramic sourcing to excessive thermal gradients. A review of the RF design can be found in [2].
In response to this, RadiaBeam has developed a novel
design that employs a coaxial window, instead of cylindrical. This approach provides several benefits. First, the diameter of the coaxial line is defined by the RF power notfrequency since it operates in Transverse Electro-Magnetic(TEM) mode. The window size can be reduced to approximately 250 mm which significantly reduces the fabrication complexity and improves structural stability. Second,
water cooling can be applied to both inner diameter (ID)and outer diameter (OD), instead of just the OD of the cylindrical window. Therefore, the field distribution in the___________________________________________* This work was supported by the U.S. Department of Energy, Office ofBasic Energy Science, under SBIR grant DE- SC0021552† kutsaev@radiabeam.com
TUPB: Tuesday Poster Session
MC4.5 Other technology

Figure 1: Cross-section view highlighting major sub-assemblies and components.
The window sub-assembly features the critical ceramic
window braze. Additional details regarding the Titanium
Nitride (TiN) coated Kyocera AO479U window can befound in prior publications [3, 4]. The parts brazed to theinner diameter of the ceramic form a cooling channel thatplaces all braze joints on the air side of the assembly toeliminate risk of water to vacuum leaks. The sleeve that
forms the hermetic seal with the metallized ceramic innerdiameter is 1.27 mm thick. This allows the sleeve to deform
during the high temperature braze to absorb the residual
stress caused by the differential coefficients of thermal expansion (CTE) between copper and alumina. Additionally,
the thin wall provides excellent heat transfer characteristics.
The outer diameter of the ceramic is brazed to anotherthin wall sleeve. During brazing, tooling constricts the thinwall to control the growth of the copper sleeve and the gap
between the sleeve and the outer diameter of the ceramicat brazing temperatures. Without constrictive tooling, thedifferential expansion between the copper and alumina
would result in a ~1.52 mm gap, far beyond the .025-.076
mm gap required for liquid braze alloy to be pulled into thejoint via capillary action. Similar approaches have been
demonstrated throughout literature [5-7]. Components
TUPB099
515

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ENGINEERING DESIGN OF 402 MHz NORMAL CONDUCTING COAXIAL
WINDOW*32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-TUPB100

S. U. Thielk†, R. Agustsson, S. Kutsaev, A. Pronikov, A. Martinez
RadiaBeam LLC, Santa Monica, CA, USA
J. Vennekate, G. Ciovati, R. Rimmer
Thomas Jefferson National Accelerator Facility, Newport News, VA, USA
Abstract
RadiaBeam has designed a 915 MHz, 25 kW CW Fundamental Power Coupler (FPC) to power a Nb3Sn coatedsuperconducting radio-frequency (SRF) cavity. Unlike traditional FPCs for SRF cavities, the device relies only on
conductive cooling by cryocoolers. The baseline design
was adapted from the liquid helium cooled 805 MHz SNS
FPC with the notable addition of an intermediate 50 K thermal intercept and associated RF shield. Engineering design
details to address the thermomechanical, manufacturability, and structural challenges will be presented. Particularemphasis will be placed on static and dynamic heat load
management along with finite element analysis to validate
mechanical stability. Additionally, initial manufacturing
studies of the coaxial window brazing will be discussed.

INTRODUCTION
The design complexity of an FPC is rooted in the strictvacuum, thermal and mechanical requirements while ensuring the manufacturing complexity and risk is minimized. Further, these efforts must be performed iteratively
with RF design to ensure efficient power coupling into acavity. Although this paper is not focused on RF design, it
is pertinent to note that the FPC is designed to operate at
915 MHz with a S11 = -50.17 dB, S21 = -.006 dB and a Qfactor between 2.96e6 to 3.3e6 with the intended Nb3Sn
coated SRF cavity. Similar to the SNS approach [1], a doorknob transition and coaxial style window were used.
A key requirement of the FPC is to transition from cryogenic temperatures near the cavity to the room temperaturecryostat while minimizing the heat load to the cooling systems. In addition to the static heat transfer, heat generated
from RF losses and radiation must be accounted for. SRF
cavities fabricated from pure niobium operate around 2 K,
typically achieved with complex and costly liquid helium
systems. Nb3Sn coated SRF cavities can operate with low
losses at ~4 K, permitting the use of cryocoolers and conduction based heat removal. Without the option to routeliquid helium near the FPC to cavity connection, a 50 K
intercept linked to the first stage of the cryocooler can be
employed. In this effort, the required heat loads were___________________________________________* The work was supported by U.S. Department of Energy, Office of Science, Office of Nuclear Physics via a grant from the Accelerate Innovations in Emerging Technologies program and by DOE-ARDAP via a
grant from the Accelerator Stewardship program. The contribution fromJLab is based upon work supported by the U.S. Department of Energy,
Office of Science, Office of Nuclear Physics under contract DE-AC0506OR23177† sthielk@radiabeam.com

TUPB: Tuesday Poster Session
MC4.8 Superconducting RF

defined as <2 W and <50 W to the SRF cavity and to the
50 K intercept, respectively. All of these factors make FPC
design a multi-disciplinary effort as documented elsewherein more comprehensive design overviews [2, 3].

MECHANICAL DESIGNThe FPC fabrication can be divided into three primarysub-assemblies as shown in Fig. 1: the doorknob, window,
and outer conductor. The doorknob is responsible for transferring power from a WR975 rectangular waveguide into a
coaxial port for the FPC. It consists of a welded aluminumbox containing the copper doorknob and inner and outerconductor extensions. The window sub-assembly serves as
the atmosphere to vacuum barrier, includes the critical
fixed length antenna, and provides diagnostic ports. The
positioning of the antenna tip is critical to the power coupling. Therefore, there are clear advantages to include
methods to adjust the position. However, a fixed length antenna was elected as the most effective approach after comparing system requirements to manufacturing complexity.
The outer conductor assembly connects the flange bolted
to the cavity to the window and cryostat wall. The temperature gradient across the outer conductor sub-assemblycomponents is accomplished by a thin-walled thermal
choke and an RF shield.

Figure 1: Cross-section of complete FPC assembly highlighting key features.
The RF shield concept was inspired by multiple publications [4- 6]. Serving as the outer conductor starting at the
50 K intercept, there is a small gap between the end of theshield and the 4.2 K cavity flange, as shown in Fig. 2. Eliminating this conduction path funnels heat from RF losses
close to the cavity to the higher capacity 50 K cryocooler
circuit. A small lip was added to the tip of the shield, maintaining the effectiveness while alleviating concerns about
manufacturability and potential interference.

TUPB100
519

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DESIGN OF A 25 kW FUNDAMENTAL POWER COUPLER FOR
CONDUCTION COOLED NB3SN INDUSTRIAL LINAC*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-WEXA001

M. Sato†, Z. Fang, Y. Fukui, K. Futatsukawa, K. Ikegami, H. Kobayashi, C. Kubota, T. Kurihara,
T. Miura, F. Naito, K. Nanmo, T. Obina, T. Shibata, T. Sugimura, A. TakagiHigh Energy Accelerator Research Organization (KEK), Ibaraki, Japan
H. Kumada, Y. Matsumoto, S. Tanaka, University of Tsukuba, Ibaraki, Japan
T. Ohba, N. Nagura, NAT, Ibaraki, Japan
T. Toyoshima, ATOX, Ibaraki, Japan
H. Oguri, Japan Atomic Energy Agency, Ibaraki, Japan
Abstract
Accelerator-based boron neutron capture therapy(BNCT) has been studied worldwide. The iBNCT (Ibaraki
BNCT) project began in collaboration with KEK, the University of Tsukuba, Ibaraki Prefecture, and related privatecompanies in Japan in 2010. The iBNCT project aims torealize linac-based BNCT by irradiating a beryllium target
with protons accelerated to 8 MeV. The accelerator configuration comprises an ECR ion source, a 3-MeV radio-frequency quadrupole linac, and an 8-MeV Alvarez-type drift
tube linac, which is based on the Japan Proton Accelerator
Research Complex linac techniques. The iBNCT project
has achieved stable operation with an average proton beam
current of 2 mA with a repetition of 75 Hz and a beamwidth of 0.92 ms. After the completion of the non-clinicalstudies in the fiscal year 2022, we finished preparing tostart a clinical study in the year 2023 for both the medical
and accelerator sides. The iBNCT project began as a PhaseI Investigator-initiated clinical trial in January 2024. In thispaper, the current status of the iBNCT accelerator and its
prospects are discussed.

INTRODUCTION
Accelerator-based boron neutron capture therapy(BNCT) has been extensively studied in recent years as anovel cancer therapy. It has a long history of clinical research on nuclear reactors; however, medical treatments innuclear reactors cannot be a general treatment owing toconstraints on its operation and management. Therefore, an
accelerator-based BNCT has gained popularity. The
iBNCT project was launched in 2010 in collaboration with
the University of Tsukuba, High Energy Accelerator Research Organization (KEK), related private companies, andIbaraki Prefecture in Japan [1]. The iBNCT project aims torealize accelerator-based BNCT with the accelerator configuration of 3-MeV radio-frequency quadrupole (RFQ)
linac and 8-MeV Alvarez-type drift tube linac (DTL),
whose feasibility has already been proven in the Japan Proton Accelerator Research Complex (J-PARC). Figure 1
shows a schematic of the iBNCT accelerator. The apparatus was installed at the Ibaraki Neutron Medical Research Center in Tokai, Ibaraki Prefecture, Japan. A bird’seye view of the iBNCT accelerator can also be found in

Ref. [2]. Assuming that all the accelerator configurations
are installed in a hospital, the size of the entire systemshould be as small as possible. As shown in Fig. 1, the proton beam passes from left to right. The primary proton
beam was generated using an ECR ion source (ECR-IS)
and accelerated to 50 keV under an electro-static field of
50 kV. The ECR-IS is driven by a 2.45-GHz magnetronwith a maximum RF power of 3 kW. After the low-energy
beam-transport line (LEBT), a 3-MeV RFQ is placed. The
RFQ design was based on the J-PARC RFQ-II [3]. A
324 MHz klystron provides RF for both the RFQ and DTL
simultaneously [4]. The typical rated power is 340 kW for
the RFQ and 320 kW for the DTL. The medium-energy
beam-transport line (MEBT) between the RFQ and the
DTL contains three permanent quadrupole magnets and abeam-position monitor. After the MEBT, the DTL is placed.
The design of the DTL is also based on the J-PARC DTL;
however, it differs from the J-PARC DTL in its length andquadrupole magnets in the drift tubes. In the iBNCT accelerator, the output energy is optimized to be 8 MeV; thus,
the length of the DTL is only 3.1 m. Another point is theapplication of permanent magnets for the quadrupole ineach drift tube to save on electricity costs. A beam transportline (BT) of approximately 15 m in length was located after
the DTL. In the straight line immediately before the neutron-generation beryllium target, a beam expander, which
comprises two quadrupole and two octupole magnets, is installed alternative to expand the beam lateral size and reduce the beam intensity per unit area on the target. The beryllium target has a three-layer structure comprising
0.5-mm thick beryllium, 0.5-mm thick palladium, and
10-mm thick copper. A detailed description is provided inRef. [5, 6]. The neutron moderator and collimator were located after the beryllium target. This apparatus not only decreases neutron energy generated by 9Be(p, n) reaction
from a few MeV to the epi-thermal neutron region below
10 keV but also suppresses unwanted -rays and high-energy neutrons for BNCT. Guidelines have been establishedby the IAEA for the desired neutron flux for BNCT, which
requires an intensity of more than 1×109 n/cm2/s [7].
Therefore, high proton beam intensity is required. Thus,
the iBNCT accelerator must be designed with a higher proton beam intensity than that of the J-PARC accelerator,
which forms the basis for the design.

___________________________________________† masaharu.sato@kek.jp

WEXA: Main Session WEX
MC3.1 Industrial and medical accelerators

WEXA001
523

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STATUS OF THE iBNCT ACCELERATOR

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-WEXA002

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

ADVANCES IN FS SYNCHRONIZATION
M. K. Czwalinna∗ , J. Branlard, B. Lautenschlager, F. Ludwig, S. Schulz, H. Schlarb
Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
Abstract
Linear accelerators for FELs have very high requirements
for the accuracy of synchronization. The long and short term
stability is influenced by various sources of interference. In
this paper it will be shown which methods of stabilization
exist and how synchronization accuracy up to the single-digit
femtosecond-level can be achieved.

INTRODUCTION
High precision applications at Free-Electron Lasers (FEL)pose demanding requirements on the involved reference distribution and control systems of the Linear electron accelerators (Linac). Stability requirements for the Linac arederived from the needs of user experiments, concerning
photon energy stability, and the desired temporal resolution when observing dynamics on the femtosecond scale.
Advanced FEL schemes as the hard x-ray self seeding, arehighly sensitive to deviations from the ideal electron bunchproperties in both, the transverse and longitudinal phasespace. All large-scale FEL facilities require some sort ofsynchronization system to reach sufficient time and phasestability. Experiments in pump-probe configuration with
two or more radiation sources (x-ray photons, optical laser,THz) are limited in achievable measurement resolution bypulse widths and relative timing stability in between thepump and probe pulses.
All phase-critical subsystems at a Linac are susceptible forenvironmental changes, including variation of the ambient
temperature, changes in relative humidity and air pressure(in case of laser systems), as well as micro-phonics andother types of vibrations and ground motions. In addition
to the performance demands, at user facilities also the robustness and reliability of the critical subsystems is a vital
property to guarantee a long mean time between failuresand high availability. Costs for installation, operation andmaintenance are additional criteria. When selecting a typeof synchronization system, it makes sense to consider all of
the mentioned aspects. Therefore, at most facilities a hybrid
solution has been realized, providing a combination of an
RF-based distribution for shorter distances, and a long-haullaser-based synchronization system to fulfill the needs of themost timing critical client systems at an FEL.

SYNCHRONIZATION TECHNIQUES
Each of the possible synchronization techniques comeswith its own challenges, advantages and drawbacks. For
example, RF-based distribution systems have relatively low
costs for small facilities and can provide many reference tap∗ marie.kristin.czwalinna@desy.de

WEXA002528

points for the RF cavity control. However, their critical parameters concern phase drift in cables, phase uncertainties offrequency dividers and ability to recover phase offsets after
power cycling of the system [1]. To improve the stability ofa passive RF distribution system one has to carefully choose
cabling type with temperature coefficients of <20 fs m−1 K−1and an optimal ambient operation temperature to minimize
drifts induced by temperature variation [2]. In addition,
it might be needed to actively reduce overall temperaturefluctuation in the whole accelerator tunnel during operation.
Passive RF-distribution systems can achieve a long-term
stability of about 50 fs/day/100m [3]. However, compared
to telecom optical cables, RF cables suffer with typically
3 dB/100m from power loss. For long-haul distribution systems, this requires a lower distribution frequency with local
frequency and phase reconstruction, to reduce distortions
along the accelerator. A purely RF-based synchronization
with an interferometric phase reference line and active stabilization is under development and has demonstrated alreadya phase error as good as ±200 fs over several days for shortlinks of <200 m [4, 5].
Another approach are pure continuous wave (CW) optical links for distributing a microwave reference frequency
over optical fiber, either as amplitude modulated (AM) or
frequency modulated (FM) signal. As alternative to RF oscillators also CW optical lasers or atomic clocks can serve as
ultra-low noise phase reference system. CW optical systems
come with the advantage of usually lower costs while stillreaching timing jitter performance as good as 10 fs level. For
mitigating long-term timing drifts to below <1 ps over days,a more complex implementation has to be considered, e.g.
by using multiple fibers for the same link (one uni-directional
and a bi-directional link) for re-calibration purpose [6,7]. An
RF-over-fiber reference distribution system has been developed for LCSL as described in [8]. It achieved an integrated
residual jitter of 17.5 fs (10 Hz to 10 MHz) for a transmitted 476 MHz reference frequency. The limitation of CW
reference sources in general are given by the fact that they
deliver only a single frequency, reducing the variety and also
the performance when phase-locking client systems to thereference source.
At SwissFEL, a CW-optical system for connecting most
systems (remote microwave oscillators) has been chosen,
showing less than 40 fs drift peak-to-peak over 24 h and lessthan 10 fs rms (10 Hz to 10 MHz) integrated jitter [9, 10]. A
few pulsed optical links were added for the use of electrooptical bunch arrival time monitors, and for applying a directlaser-to-laser synchronization for the user experiments.
Such pulsed optical synchronization systems are required
to fulfill highest demands on timing stability, in terms ofjitter and drift, but also typically require highest investment
WEXA: Main Session WEX
MC4.1 Beam diagnostics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-WEXA005

A. Scheinker† , Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract
Machine learning (ML) tools have been growing in popularity for accelerator applications, but still struggle with timevarying systems, for which they require lengthy brute-force
re-training. LANL has developed machine learning (ML)based tools, that utilize adaptive model independent feedback control theory together with hard physics constraints, tomake the tools much more robust to distribution shift. These
adaptive ML tools can extrapolate much further beyond thespan of the training data and are thus much more robust for
time-varying systems. This talk will give a broad overview
of the challenges of various time-varying accelerator systems at various accelerator facilities (known as systems with
distribution shift in the ML community) and will present
adaptive ML tools for 6D phase space diagnostics of intense
charged particle beams. The talk will also give a general
overview of adaptive latent space tuning, which is the novel
method we have developed for adaptive ML, and how weare strictly enforcing hard physics constraints in our ML
tools, which traditional ML tools lack. We demonstrate
our general methods for various accelerators: the 5-meterlong ultra-fast electron diffraction (UED) HiRES compact
accelerator at LBNL, the kilometer long plasma wakefield
accelerator FACET-II at SLAC, and the LANL ion accelerator LANSCE.

INTRODUCTION
Particle accelerators are large complex systems composedof thousands of coupled components including resonant radio frequency (RF) structures for beam acceleration andmagnets for beam shaping and steering. The performance of
all of these components drifts with time due to external disturbances such as environmental temperature variation, vibrations and power line fluctuations, due to ageing, and due tomisalignment and shift of components during maintenance.
Furthermore, the beams themselves have time-varying initial conditions due to time variation of the complex beamsource properties. Changing initial conditions can strongly
effect the detailed 6D phase space distributions of beams,
especially for intense beams whose evolution is governed bycomplex collective effects such as space charge forces andcoherent synchrotron radiation.
Alongside the complexity and time variation of these systems and their beams, there is a lack of detailed non-invasive
beam diagnostics beyond simple 1D measurements such as
beam position monitors, beam current monitors, or beam
∗ This work was funded by the US Department of Energy (DOE), Of-

fice of Science, Office of High Energy Physics under contract number
89233218CNA000001 and the Los Alamos National Laboratory LDRD
Program Directed Research (DR) project 20220074DR† ascheink@lanl.gov
WEXA: Main Session WEX
MC4.1 Beam diagnostics

loss monitors. The result is that accelerator beams are difficult to tune up after an outage (typically requiring weeks
of effort be large teams) and are difficult to re-tune between
different experiments even when the machines are running.
Besides the large amount of time that is consequently wasted
in re-tuning of the machines, they are also typically runningat sub-optimal states with operators chasing drifts to decrease beam loss by tuning tens-hundreds of parameters byhand based on experience.
Motivated by the above, there has been a strong effort tocreate new tools for beam diagnostics and controls. For the
EuXFEL, a convolutional neural network-based approachhas been developed for generating high-resolution longitudinal phase-space (LPS) (𝑧, 𝐸) images of the electron beam [1].
Convolutional neural networks have also been combine withdestructive beam measurements to develop extremely fast
virtual diagnostics for 4D tomographic phase space reconstructions [2]. Neural network-based methods have also
been developed for predicting the transverse emittance of
space charge dominated beams [3]. Convolutional neuralnetworks and clustering algorithms have also been developed for predicting the longitudinal phase space of FEL
beams and also to cluster these images to highlight patterns
within the data [4]. Recently, very interesting methods havealso been studied for phase space reconstructions based on
normalizing flows [5]. One benefit of all ML-based tools isthat they are by default fully differentiable models, enablingeasy studies of complex input-output dependencies.
The time variation of the systems makes it clear that offthe-shelf machine learning methods cannot simply be usedas they will require continuous repeated re-training basedon expensive invasive beam measurements if they are applied to such systems which quickly vary with time. To
overcome this difficulty, a new class of adaptive machine

Figure 1: Adaptive latent space tuning setup in which a generative autoencoder generates all 15 projections of a beam’s
6D phase space and then only those projections that can bemeasured non-invasively are compared to their predictions
in order to track the time-varying beam with unknown andtime-varying initial condtions, by adaptively tuning the lowdimensional latent embedding.
WEXA005
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ADAPTIVE MACHINE LEARNING WITH HARD PHYSICS CONSTRAINTSAND GENERATIVE DIFFUSION FOR 6D PHASE SPACE DIAGNOSTICS∗

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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S. U. De Silva†, Old Dominion University, Norfolk, VA, USA
Abstract
The International Liner Collider requires a crabbing system to increase the luminosity of the colliding electron
bunches. The ILC has a large crossing angle that requires
compensation in order to meet the luminosity requirements. There are several frequency options proposed forthe crabbing cavity design. Two crab cavity designs wereselected to be prototyped in the pre-lab phase, following
the Down Selection Review on Crab Cavity Design held in
April 2023. The two rf designs selected are the 1.3 GHz rfdipole cavity and the 2.6 GHz QMiR cavity. This paper describes the electromagnetic and mechanical design detailsof the two compact crabbing cavity designs.

INTRODUCTION
The International Liner Collider (ILC) is designed tocollide electrons and positrons at the speed of light withcenter of masses (CoM) varying from 250 GeV to 1 TeV.
The baseline design CoM is 250 GeV where the 1 TeV
beam energy is the proposed upgrade of the ILC. The two
beams are accelerated in two separate linacs spanning over
20 km as shown in Fig. 1 [1, 2].

Figure 2: Luminosity degradation as a function of crossing
angle for ILC.

Figure 3: Crab crossing with crabbing systems for electron
and positron beams.
Figure 1: Layout of the Electron-Ion Collider.
The expected integrated luminosity goal of the ILC is~1034 cm-2sec-1. The ILC requires crabbing cavities to compensate for the luminosity degradation due to the large
crossing angle of 14 mrad. Operation without crab cavities
may lead to a luminosity reduction up to 80% as shown in
Fig. 2. The crabbing cavities will deliver a transverse kickat the head and tail of the colliding bunches that will rotate
the bunches allowing them to overlap them at the interaction point (Fig. 3) [3]. This maximizes the luminosity byincreasing the number of interactions between the particles
in each colliding bunch. Crabbing systems will be installed
in both electron and positron beams and does not require
crabbing systems to cancel the crabbing effect.

ILC Crab Cavity Requirements
The crabbing system specifications include dimensional
constrains and rf requirements as listed below [4].
Dimensional Constraints:
 Total beam line space – 3.8 m
 Separation between two beam lines < 197 mm (Fig. 4)
 Minimum crab cavity beam aperture – 25 mm___________________________________________* This research used resources of the National Energy Research Scientific Computing Center (NERSC); a U.S. Department of Energy Office of
Science User Facility operated under Contract No. DE-AC0205CH11231.
This work was produced by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy.
† sdesilva@jlab.org
WEXA: Main Session WEX
MC4.5 Other technology

Figure 4: Beamline layout of the crabbing system.
WEXA006
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CRABBING CAVITY SYSTEM DEVELOPMENT FOR INTERNATIONAL
LINEAR COLLIDER *32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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THE DEEP ELECTRON FLASH THERAPY FACILITY
C. Rossi∗ , M.E. Angoletta, O. Brunner, J. Bauche, R. Corsini, J.M. Cravero, S. Doebert, B. Frisch,
E. Granados, A. Grudiev, R. Key, V. Korchevnyuk, A. Latina, A. Malyzhenkov, I. Syratchev, P. Wang,
W. Wuensch, CERN, Geneva, Switzerland
C. Bailat, F. Bochud,T.T. Böhlen, J. Bourhis, J. Damet, L. Desorgher, T. Garvey, J.F. Germond,
W.R. Geyer, V. Gregorio, V. Grilj, F. Herrera, R. Moeckli, N. Walter
CHUV, Lausanne, Switzerland
S. Curtoni, T. Dufour, P. Liger, THERYQ, Rousset, France
Abstract
The “FLASH” effect is currently a topic of considerable
interest in radio-oncology. We present the design of a novel
VHEE linac, to be built and installed at CHUV (Lausanne),
capable of producing electron beams which deliver radiation
at dose rates and time scales consistent with the FLASH
effect. The design is based on X-band radio-frequency technology, developed at CERN for the CLIC study. The e-beamproperties correspond to a CHUV specification and would
allow large, deep seated, tumours to be treated. Constructionof DEFT (DEEP Electron FLASH Therapy) will be assured
by the company THERYQ in the context of a CHUV-CERNTHERYQ collaboration.

INTRODUCTION
Radiation therapy (RT) constitutes one of the main pillars
in cancer treatment, together with surgery and chemo/immuno therapy [1–3]. The conflicting requirement of sparing
the healthy tissues that surround the tumor while maximizing
the effectiveness in tumor control has pushed RT technologies towards fractionated dose administration together withhighly conformal dose delivery systems. Besides MV photon
beams, which are the workhorse of modern external beamRT, other therapeutically used particle species include protons, light ions, and electrons <25 MeV. While such modern
high-precision RT treatments can provide acceptable clinicaloutcomes with limited side effects for many patients [1, 3]
there is still a clinical care gap and a resulting clinical needfor numerous cancer patients.
For such cases, hope is being generated by the observationthat doses delivered at ultra-high dose rates (UHDR, average
dose rate ≳50 Gy/s) can produce a sparing effect on healthy
tissues while maintaining the effectiveness on tumoral cells
compared to irradiations delivered at conventional dose rates(average dose rate ∼0.05 Gy/s) [4, 5]. This increase of thetherapeutic index by the ultra-fast dose delivery, commonlyreferred to as “FLASH effect”, was initially observed inthe 70’s, first proposed in 2014 and has since then been
independently confirmed in numerous studies using different
radiation modalities and preclinical models [4–7].
The adoption of the high-gradient RF technology developed at CERN for the realization of the high-energy linear
collider CLIC appeared to be the logical choice for designing∗ carlo.rossi@cern.ch

WEYA002544

a compact FLASH-RT device capable of producing penetrating very high-energy electron (VHEE, 100 - 250 MeV)
beams at UHDR to treat deep-seated tumors. In addition,
supporting experiments are being carried out at the CERN
facility CLEAR in relation to the creation and detection of
UHDR and to the characterization of the FLASH effect.

MEDICAL BACKGROUND
The potential implications of FLASH-RT in clinical practice are profound. Conventional radiotherapy, while effective, often necessitates a delicate balance between deliveringsufficient doses to eradicate tumors and minimizing exposure to surrounding healthy tissues. This balance becomes
particularly challenging when treating tumors located close
to critical structures and/or large and non-curable cancers
such as glioblastomas for which there is a huge unmet clinical need. FLASH-RT, on the other hand, with its potential
to elicit a biological selectivity between tumors and healthy
tissues, may offer a breakthrough in overcoming these limitations. The reduced toxicity induced by the FLASH effect on
the healthy tissue could allow for higher therapeutic doses,
potentially improving either local control and overall survival rates or reducing treatment side effects for challenging
cancers.

Status of Preclinical and Clinical FLASH
Research at CHUV
Extensive preclinical evidence supports the potential of
FLASH-RT to enhance the therapeutic ratio of RT by delivering treatments at UHDR [5–7]. In 2018, CHUV successfully
conducted the first human treatment using UHDR electrons,
marking a significant milestone in the clinical applicationof FLASH-RT [8, 9]. The patient, treated for cutaneous lymphoma, showed excellent tumor control with minimal side
effects, demonstrating the feasibility and potential benefitsof FLASH-RT in clinical settings. Building on this success, CHUV has initiated two human clinical trials: a dose
escalation trial (IMPulse, NCT04986696) for metastasizedmelanoma and a Phase II trial (LANCE, NCT05724875)
aimed at evaluating the treatment of localized cutaneous
squamous cell carcinoma (SCC) and basal cell carcinoma(BCC) with FLASH-RT in comparison with standard of careRT. Both trials show promising preliminary outcomes.
WEYA: Main Session WEY
MC2.5 Industrial and medical accelerators

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RESULTS FROM CXLS COMMISSIONING
W. S. Graves∗ , G. Babic, C. V. Bell, S. Botha, T. Brown, B. Cook, T. Dela Rosa, A. Dupre,
K. Eckrosh, E. Everett, J. Falconer, P. Fromme, A. Gardeck, M. Holl, M. Hussain, S. Jachim,
R. Jaswal, P. Jiang, R. Kaindl, R. Kirian, R. Larsen, H.-S. Lee, B. Liebich, H. Loos, X. Ma,
L. Malin, A. Martinez, S. Rednour, A. Ros, E. Ros, A. Sandhu, A. Semaan, D. Smith, J. Stanton,
S. Teitelbaum, S. Tilton, J. Tinlin, S. Tripathi, J. Vela, Arizona State University, Tempe, AZ, USA
V. Dolgashev, S. Tantawi, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
P. D. Brown, MIT Bates Research and Engineering Center, Middleton, MA, USA
Abstract
The Compact X-ray Light Source (CXLS) is a compact source of femtosecond pulses of x-rays that is now
commissioning in the hard x-ray energy range 6-20 keV.
It collides the electron beam from recently developed
X-band distributed-coupling, room-temperature, standingwave linacs and photoinjectors operating at 1 kHz repetition
rates and 9300 MHz RF frequency with a Yb:YAG 1030
nm laser beam operating at high peak and average power at
1 kHz repetition rate with pulse energy up to 200 mJ. We
present the performance of the CXLS accelerator, laser, andtiming systems, and initial x-ray results.

INTRODUCTION
Future light sources aim to improve performance, cost,and accessibility over today’s instruments. CXLS uses inverse Compton scattering (ICS) to produce partially coherent
synchrotron-like x-ray pulses at few hundred fs duration in
the hard x-ray range. ICS-based instruments differ from the
major XFEL and synchrotron facilities as well as current
laboratory scale sources, thus require development of new
experimental techniques, sample delivery, detector properties, controls and data analysis methods that are matched totheir novel properties. These properties include lower flux
than the major facilities as well as improvements in stability
and precision of beam properties, and the ability to tailor
integrated accelerator, laser, and x-ray beamline operations
to optimize particular experiments.

CXLS INSTRUMENT AND LABS
The CXLS is constructed and now commissioning, having
produced first x-rays in February 2023. The design parameters are shown in Table 1 and the layout of the source isshown in Fig. 1. It is installed in new laboratories at ASU’s
Biodesign Institute that were carefully constructed [1] toprovide tight environmental controls and safety systems [2]for the high power equipment. Construction details include
specially selected rebar in the floors and walls for low static
magnetic fields, a Faraday room that encloses the high power
RF transmitters, water-cooled equipment racks for low-level
RF and magnet power supplies, 2 m thick floors measured at
VC-E or better vibration standards under the sensitive beamequipment, and tight controls on air and water temperatures.
∗ wsg@asu.edu

WEYA004
550

Table 1: CXLS design performance at 0.1% and 5% bandwidth. Brilliance units are ph/(s 0.1% mm2 mr2 ).
Parameter

0.1% BW

5% BW

Photon energy (keV)
Photons/pulse
Pulse rate (Hz)Avg flux (ph/s)
Avg brilliance
Peak brilliance
Round RMS src size (µm)
Round RMS src angle (mrad)
RMS pulse length (fs)
RMS timing jitter (fs)

2 - 20
5 × 106
1000
5 × 109
2 × 1012
3 × 1019
3.0
4.0
< 300
< 50

2 - 201 × 1081000
1 × 1011
5 × 1012
9 × 1018
3.0
4.0
< 300
< 50

The majority of heat is transferred to water rather than air.
Operation of the equipment has proved to be very stable asmeasured by RF phase jitter and position and timing of thebeams. The reproducibility of the beams is excellent, withshort start-up times each day.
The project has been constructed and run by a staff ofabout 20 scientists and engineers with a cohort of undergraduate students typically numbering 20, and another 5 graduate
students. Students have been involved in all stages of designand construction, and routinely operate the CXLS. Our standard operations run for 10–14 hours per day rather than 24/7
due to the limited staff size.

Accelerator and RF Systems
The accelerator consists of a 4.5 cell photoinjector [3]and three 35-cm linac sections of 20 cells each, all poweredby 2 RF transmitters as shown in Fig. 2. All of the accelerator structures are high efficiency standing-wave roomtemperature copper structures with a repetition rate of 1 kHz
and fill time of 170 ns. Peak cathode field in the photoinjector is 120 MV/m for 3 MW input power. The cathode cell isless than a half-cell so that the laser arrival timing is close
to the peak applied electric field. Exit energy is 4.0 MeV.
The linacs are innovative distributed-coupling structures [4] with a high shunt impedance 165 MOhm/m making
them very efficient, gradient up to 30 MV/m and peak surface E-field of 120 MV/m. The structures produce energy
gain of 10 MeV each for 2 MW input power and a final maxWEYA: Main Session WEY
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AUTOMATIC RETUNING OF SUPERCONDUCTING LINACSUSING LightWin
A. Plaçais∗ , F. Bouly, E. Froidefond
Univ. Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, Grenoble, France
J.-M. Lagniel, G. Normand, A. K. Orduz
GANIL, CEA/DRF-CNRS/IN2P3, Caen, France
B. Yee-Rendon, JAEA/J-PARC, Tokai, Japan
L. De Keukeleere, J. Van De Walle, SCK CEN, Mol, Belgium
Abstract
Reliability is an important feature for high-power particle
accelerators. A significant proportion of beam trips comefrom the failure of superconducting accelerating cavities ortheir associated systems. Failure compensation is a technique that can limit the impact of these failures and therefore
increase beam availability. Finding ideal compensation settings is, however, a difficult challenge that involves beam
dynamics and multi-objective optimization, and which raises
very different issues according to the linac under study. In
this study, we present the LightWin tool to automaticallyfind compensation settings in linacs. We study different
compensation strategies on the MINERVA superconducting
linac and present our first results on the SPIRAL2 superconducting linac.

CAVITY FAILURE COMPENSATION
FOR HIGH AVAILABILITY
In order to advance the frontiers of particle physics anddevelop new applications, hadron accelerators are being
driven towards increasing mean beam power. This tendency
gives rise to numerous issues concerning accelerator design. These systems are expensive, making it important tomaximize beam availability. To increase the RF-to-beamefficiency, reach higher accelerating fields, and optimize
operation costs, the accelerating systems generally utilize
superconducting (SC) technologies. However, these systems
involve more subsystems which increase the failure risk.
Failure of cavities or their associated systems is a significant source of beam trips. Therefore, a promising solution
to increase beam availability lies in cavity failure compensation. When a cavity failure is detected, the cavity is quickly
detuned, and neighboring or all RF cavities are retuned. Thiscan help maintain the beam and, in some cases, restore nominal beam conditions.
This method has already been applied successfully [1–3].
However, finding compensation settings for a given failure
scenario can be complex and time-consuming. Additionally, this method is relatively new, and best practices forcompensation are not well established. Furthermore, thefailure compensation strategy may differ from one machine
to another. This strategy depends on the linac design characteristics (e.g., longitudinal acceptance) and its purpose(type of beam and reduced velocity). Margins – foreseen by
design, especially on the accelerating gradient – will alsoease the application of the failure compensation scheme.
This is generally the case for Accelerator-Driven Systems(ADS). They are nuclear fission reactors driven by a stable
proton beam. The beam impacts a spallation target, producing neutrons and interacting with the sub-critical nuclear
core. Every prolonged interruption of the beam creates thermal constraints on the reactor structure. These interruptions
also necessitate lengthy restart procedures, further reducing
plant availability [4]. Thus, ADS feature a fault-tolerance
design based on redundancy. The cavities are operated derated to their maximum capabilities, and the longitudinal
acceptance of the linac is maximized by design. The requirements may differ from one project to another, but generally
one should be able to recover the beam after a failure in a
few seconds [5].
Considering the importance of reliability studies, thededicated ReFilL (Reliability and fast Failure compensation methods in RF superconducting Linacs) project was
launched at CNRS – IN2P3. Its objectives are to develop
new RF failure mitigation techniques and assess the causes oflongitudinal acceptance reduction – in particular, non-linear
effects and parametric resonances in high gradient linacs [6].
The initiative currently involves the LPSC Grenoble, IJCLab
Orsay and GANIL Caen French laboratories.
In the first section, we introduce the LightWin code andprovide general implementation details. LightWin is a beam
dynamics code developed for finding compensation settings
in SC linacs. The goal is to provide a tool that can adapt
to any linac to study different compensation strategies. The
following sections present examples of studies and working perspectives for different linacs. The second section isdedicated to a systematic study on MINERVA. In the third
section, we present the specific challenges of the SPIRAL2
SC linac, as well as the initial settings we found for a cavity
failure in the low-𝛽 section.

LightWinLightWin is an open-source code we developed for finding
compensation settings [7–9]. It is mainly written in Python.
It was designed with the ultimate goal of being usable on
any linac, with any cavity failure compensation strategy. Its∗ placais@lpsc.in2p3.fr

THXA001556

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MATCHED TRANSPORT OF INTENSE AND COASTING BEAMS
THROUGH QUADRUPOLE CHANNELS
C. Xiao∗ , L. Groening
GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany
Abstract
Imposing angular momentum to a particle beam increases
its stability against perturbations from space charge. In orderto fully explore this potential, proper matching of intense
coupled beams along regular lattices is mandatory. Herein, anovel procedure assuring matched transport is described andbenchmarked through simulations. The concept of matchedtransport along periodic lattices has been extended from
uncoupled beams to those with considerable coupling between the two transverse degrees of freedom. For coupledbeams, matching means the extension of cell-to-cell periodicity from just transverse envelopes to the coupled beam
moments and to quantities being derived from these.

INTRODUCTION
Preservation of beam quality is of major concern for acceleration and transport especially of intense hadron beams.
This aim is reached at best through provision of smooth andperiodic beam envelopes, being so-called matched to theperiodicity of the external focusing lattice. For the time
being, the quality of matching has been evaluated throughthe periodicity of spatial beam envelopes. This is fully sufficient as long as there is no coupling between the phase spaceplanes (for brevity “planes”), neither in beam properties nor
in lattice properties.
The TRACE-2D code [1] is well suited to provide for amatching beam line between a given initial beam matrix
and a desired exit beam matrix even for a full 4D scenario.
However, it is an intrinsic property of the periodic-solution
problem that the initial beam matrix at the entrance of theperiodic channel is unknown. Accordingly, this code cannot
be applied to the present scenario in a straightforward way.
This paper aims to demonstrate that a 4D-periodic cell-bycell solution exists and demonstrates its derivation [2].
Coupled beams inhabit ten independent second-order rms
moments. They are summarized within the symmetric beam
moments matrix
⟨𝑥𝑥⟩
⎡ ′
⟨𝑥
𝑥⟩
𝐶 ∶= ⎢⎢⟨𝑦𝑥⟩⎢⎣⟨𝑦′ 𝑥⟩⟨𝑥𝑥 ′ ⟩⟨𝑥 ′ 𝑥 ′ ⟩⟨𝑦𝑥 ′ ⟩⟨𝑦′ 𝑥 ′ ⟩⟨𝑥𝑦⟩⟨𝑥 ′ 𝑦⟩⟨𝑦𝑦⟩⟨𝑦′ 𝑦⟩⟨𝑥𝑦′ ⟩⎤⟨𝑥 ′ 𝑦′ ⟩⎥,⟨𝑦𝑦′ ⟩ ⎥⎥⟨𝑦′ 𝑦′ ⟩⎦(1)

and four of its elements quantify beam coupling. Beams are
𝑥-𝑦 coupled if at least one of these elements is different fromzero.
The beam line being used to determine the periodic solution of an intense coupled beam along a periodic channel issketched systematically in Fig. 1.
∗ c.xiao@gsi.de

THXA003562

Figure 1: The beam line comprises three parts: (I) coupling production section; (II) matching section; (III) regularquadrupole doublet section (twelve cells). Space charge
effects are not considered along the first two sections (seetext).
At the beginning of the beam line, an uncoupled beam isassumed with beam sigma-matrix 𝐶 (𝑠0 ). The beam matrix
at the beginning of the matching section is
𝐶 (𝑠1 ) = ℘ ⋅ 𝐶 (𝑠0 ) ⋅ ℘T ,(2)and ℘ indicates the transfer matrix of the coupling section.
In order to obtain a periodic solution for this coupledbeam, the details of the matching section are not required as
seen in the following. However, it is modeled by a transport
matrix including 16 elements (in units of m and rad)𝑚
⎡ 1
𝑚
ℜ (𝑚1 , 𝑚2 , … , 𝑚16 ) = ⎢⎢ 5
⎢ 𝑚9
⎣𝑚13

𝑚2
𝑚6
𝑚10
𝑚14

𝑚3
𝑚7
𝑚11
𝑚15

𝑚4
⎤
𝑚8 ⎥
.
𝑚12 ⎥⎥
𝑚16 ⎦(3)

Although initially being unknown, the 16 elements mustensure that ℜ is symplectic. For brevity, the set of
𝑚1 , 𝑚2 , … , 𝑚16 shall be denoted by ℵ.

MODELLING OF PERIODIC CHANNELFor zero current, the effective focusing forces are given
solely by the external lattice. The actual beam shape has noinfluence on them and therefore the periodic solution even forcoupled beams may be found analytically. For intense beams
instead, defocusing space charge forces depend on the beam
shape and orientation in real space. Actually, they depend
also on the spatial distribution. However, since modelling ofspace charge forces using rms-equivalent KV-distributions
proofed to work very well for matching purposes, this approach is followed here as well.
The periodic solution (zero current) meets the condition
𝐶 (𝑠2 ) = ℑ ⋅ 𝐶 (𝑠2 ) ⋅ ℑT ,(4)

and the transport matrix from the exit of the coupling section 𝑠1 to the exit of the first cell is℧ (ℵ) = ℑ ⋅ ℜ (ℵ) ,(5)

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MACHINE-LEARNING-ASSISTED BEAM TUNING AT FRIB∗
K. Hwang† , Tomofumi Maruta, Tong Zhang, Qiang Zhao, Alexander Plastun, Kei Fukushima,Peter Ostroumov, Facility for Rare Isotope Beams, East Lansing, USA
Abstract
Facility for Rare Isotope Beams (FRIB) requires diverse
primary ion species beams to produce rare isotopes. The
beam tuning time can be reduced by employing Machine
Learning (ML) techniques. In this paper, we aim to explore practical perspectives on shortening beam tuning time.
Specifically, we discuss customization of Bayesian Optimization for maximum beam time utilization, and virtual
diagnostics that are currently under development.

INTRODUCTION
Each experiment at FRIB requires a different ion species
for the primary beam. This makes the efficient beam tuning
particularity import to provide more beam time for science.
We have developed high-level applications for beam tuning
based on simulation of beam dynamics, classical optimization, and Machine Learning (ML) methods. Among the ML
methods, Bayesian Optimization (BO) is routinely used andcustomized to FRIB beam tuning tasks in practical aspects
including tight beam tuning time. Virtual diagnostics using data based models are under development and expected
to significantly improve and expedite beam tuning procedures. Surrogate modeling of beam dynamics simulationis also being pursued and expected to further improve BO
performance and other applications.

Figure 1: Illustration of surrogate model assisted optimization.

BAYESIAN OPTIMIZATION (BO)Surrogate Model-Assisted Optimization
In this section, we explain how surrogate model-assisted
optimization works. Consider the problem of finding the
optimal set of controls 𝑥 ∗ that maximize an objective 𝑓 (𝑥)such that𝑥 ∗ = argmax (𝑓 (𝑥) )(1)
If we have a model 𝑚(𝑥) ≃ 𝑓 (𝑥) that can approximate thetrue objective, we can find a candidate solution 𝑥candidate =argmax (𝑚(𝑥)) that maximizes the model as illustrated inFig. 1. Next, consider a data-driven probabilistic model
𝒫 (𝑦|𝑥, 𝒟) trained on online dataset 𝒟 = {(𝑥, 𝑦 = 𝑓 (𝑥))},such that the model prediction of mean value approximatesthe objective, 𝔼𝒫 (𝑦) ≃ 𝑓 (𝑥). We can query next candidate solution 𝑥candidate that not only maximizes the modeled
objective but also explores uncertain regions far from the existing observation points. This approach, known as Bayesian
Optimization (BO), is a type of surrogate model-assisted
optimization, as illustrated in Fig. 2.
∗ Work supported by the U.S. Department of Energy, Office of Science,

Office of Nuclear Physics, under Award Number DE-SC0024707 andused resources of the FRIB Operations, which is a DOE Office of Science
User Facility under Award Number DE-SC0023633† hwang@frib.msu.edu
THXA004
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Figure 2: Illustration of Bayesian Optimization. The shaded
area represents model uncertainty, which is larger in regions
far from the observation points marked by green dots.

Why Bayesian Optimization?
We consider objectives that take from a few seconds toseveral seconds to evaluate. This includes factors such as thepower supply ramping time when transitioning from an old
control setting to a new one, which generally ranges from a
few seconds up to 30 seconds, as well as the time required
for averaging noisy measurement data. Due to the ramping
time, investing a few extra seconds in averaging can resultin more accurate and less noisy data, which in turn benefits
the training of a more precise surrogate model. Additionally,
we impose a time budget for each task, ranging from 2 to
20 minutes, depending on the problem size. This constraint
typically limits the number of training data points to fewer
than a few hundred.
Given this scenario, Bayesian Optimization (BO) is wellsuited for the following reasons. First, BO is sample-efficient,meaning it can achieve good performance with fewer data
points by strategically querying the most informative data.
Moreover, the computation time for both training and queryTHXA: Main Session THX
MC3.2 Ion linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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AN OVERVIEW OF PLASMA PROCESSING OF SRF CAVITIES AT JLAB*
T. Powers†, T. Ganey, N. Raut, I. H. Senevirathne
Thomas Jefferson National Accelerator Facility Newport News, VA
Abstract
Plasma processing is a common technique where the freeoxygen produced in a low-pressure RF plasma breaks
down and removes hydrocarbons from surfaces. This
increases the work function and reduces the secondary
emission coefficient of the treated surfaces. Jefferson Lab
has an ongoing R&D program in plasma processing. The
experimental program investigated processing using
argon/oxygen and helium/oxygen gas mixtures. The initial
focus of the effort was processing C100 cavities byinjecting RF power into the HOM coupler ports. We also
developed the methods for establishing a plasma C75
cavities where the RF power is injected via thefundamental power-coupler. As part of the processdevelopment we processed, three C100 cryomodules in our
off-line cryomodule test facility. In May 2023 weprocessed four C100 cryomodules in-situ in the CEBAF
accelerator with the cryomodules returning to an
operational status in Sept. 2023. The cumulative
improvement in field emission free operation, as measured
on a cavity by cavity basis, was 59 MeV or 24%. We
recently started processing 7 cryomodules in the CEBAF
accelerator in August 2024. Methods systems and resultsfrom processing cryomodules and individual cavities in thevertical test will be presented. Current status and futureplans will also be presented.

METHODS
Plasma processing is being explored by a number offacilities that work with superconducting cavities [1-4].
Between 2015 and 2018 it was used to process 32 cavities
in the SNS accelerator at ORNL where they achieved anaverage improvement in operational gradients of
2.5 MV/m [5]. Unlike helium processing which relies onion bombardment of the field emitters, plasma processing
uses atomic oxygen produced in an RF plasma to break
down the hydrocarbons on the surface of the cavity.
Removing this layer of dielectric material increases thework function and decrease the secondary emission
coefficient [6]. Processing of SRF cavities is done at room
temperature using a mixture of noble gas such as argon,
neon or helium and oxygen. The discharge is operated atpressures between 50 and 300 mTorr. The current gas
mixture used at Jefferson lab is 94% helium and 6%
oxygen at 300 mTorr.

Gas Supply and Vacuum Systems
Process gas was supplied by a mobile cart that had acylinder of helium or argon and a cylinder of 20% oxygen___________________________________________* Funding provided by SC Nuclear Physics Program through DOE SC
Lab funding announcement DE-FOA-0002670† powers@jlab.org
THXA005570

with the remainder of the gas being helium or argon
depending on the gas that was being used. The gas supply
system used in the vertical test area also has a cylinder of
95% argon and 5% methane which is used to“contaminate” a cavity with hydrocarbons so that we could
experiment with different processing techniques. Using aseries of valves and flow controllers we were able vary thepercentage of oxygen in the process gas as well as toregulate the flow and pressure in the cavities. Two mass
flow controllers are used; one to regulate the pressure andone to regulate the percentage oxygen. The outlet pressureof the flow controllers is appropriately 5 Torr. The pumping
system contains two turbo pumps and an RGA. In addition
to monitoring the oxygen percentages the RGA is used tomonitor the hydrocarbon fragments of H2, CO, CO2, andH2O.

Selecting RF Frequencies for Processing
For both C75 and C100 cryomodules the RF-coupling
via fundamental power coupler (FPC) is fixed and set up
for cryogenic operations of a beam loaded cavity. Thus,
when the cavity is at room temperature very little power iscoupled to the fundamental mode and pass band modes of
the cavities through the FPC. For the warm C100 cavities
the ILC style HOM couplers have relatively strong
coupling to the TE111 higher order modes, 1870 MHz to2050 MHz where the power coupled into the cavity is
between 20% and 95% of the power that is applied to the
HOM coupler.
For the C75 cavities there is moderately good couplingthrough the fundamental power coupler to the first three
TE111 modes. C75 cavities continued to use the glassy
ceramic higher order mode loads which use waveguides tocouple the HOM power out of the beam line. The cut-off
frequency for these waveguides is 1966 MHz. Above thisfrequency RF power is coupled to the HOM loads andtends to cause a breakdown in the region of the HOM
loads. Thus, we are limited to operating at frequencies
below that value. The higher order modes below thatfrequency are coupled out through the fundamental power
coupler which makes use of a half-height WR530*
waveguide and are damped by a waveguide higher ordermode filter. Said filter is replaced by a straight section of
waveguide when we perform in situ processing.
Figure 1 shows relative electric fields as determined bya set of bead-pull and S11 measurements for the threemodes that are used for processing a C75 cavity. The
1850 MHz mode has a tilt in the field pattern where thestrongest field is in the cell furthest away from thefundamental power coupler (cell 5). Fortunately, that mode
also had strong enough coupling that we could repeatedly
ignite plasma in cell 5. We did find that it was difficult togo from no plasma to plasma on in any of the cells other
THXA: Main Session THX
MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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WIDE DYNAMIC RANGE DIAGNOSTICS SYSTEM FOR PRIMARYAND SECONDARY BEAMS AT FRIB*
S. Lidia†, S. Cogan, M. Cortesi, S. di Carlo, T. Larter, A. Lokey, D. McNanney, P. Nariyoshi,
I. Nesterenko, S. Rodriguez, K. Saini, M. Smith, S. Zhao
Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI, USA
Abstract
The FRIB diagnostics system covers an extensive rangeof primary and secondary beam intensities of 14 orders ofmagnitude and requires continuous improvements. The
linac diagnostic system has provided straightforward linac
commissioning and supports the development of many primary heavy ion beam species for producing rare isotopes.
The diagnostics system for the secondary beam has aunique feature of detecting and measuring low-intensity
rare isotope beams. This talk will report on the performance of the FRIB diagnostics system and ongoing improvements.

FRIB FACILITY
The Facility for Rare Isotope Beams (FRIB) is a highpower heavy ion accelerator facility presently in operation
at Michigan State University [1]. The FRIB is a power
frontier accelerator facility aiming to provide two to threeorders of magnitude higher beam power than existing
heavy ion accelerator facilities. The FRIB linac is designed
to accelerate all stable ions to energies above 200 MeV/uwith beam power of up to 400 kW with Continuous Wave
(CW) operation (see Fig. 1), and carrying intensities up to~1013 particles per second (pps) or currents ~100 eA.
The scientific program generates demands on the functionality and operability of the facility. The ion sources andlinear accelerator, and beam transport sections for the primary beam must handle intense, low energy, ion beams
with velocities from 0.03c – 0.60c, and with mass-tocharge (A/Q) range 3 – 7. The linac acceptance is designed
to permit lossless transport of multi-charge-state beams(Q/Q ~ 1/16) [2].
While the FRIB linac operates in Continuous Wave
(CW) mode, the electrostatic chopper allows pulsed beam
operation for commissioning and tuning. As a high power
accelerator, it is important to mitigate excess beam loss
during tuning, and the chopper and beam attenuators play
key roles to this end by permitting low peak or average
power beam generation.
The high power interception devices which include theproduction target and beam dump, charge strippers andcharge selection devices must operate in regimes of large
temperature variations and thermal stresses. These are actively monitored for machine protection.

Secondary particles and rare isotopes are produced by
the interaction of the primary beam with the target. Thislarge phase space of fragments is filtered and reduced by
the fragment separator beamline and instrumentation toisolate the rare isotope of interest, which typically appear
at very low production rates.

DIAGNOSTIC ANDINSTRUMENTATION REQUIREMENTS
To support the nuclear physics program, experimental
runs are performed over periods of up to two weeks. New
runs require changes to primary beam species, energy, andintensity. To facilitate these changes, the beam diagnostics
and associated instrumentation must maintain sensitivity,
accuracy, and speed over the entire range of beam parameters. The range of beam intensities covers many orders ofmagnitude between production (1013 pps) and beam tuning(106 - 107 pps). Oftentimes, beam tuning is performed withlower duty factor (lower average power) beams, so that signal acquisition modes must allow for short pulse durations
and lower repetition frequencies.
Secondary beam production, fragment separation, andparticle identification of rare isotope species impose another set of operational demands on diagnostics and instrumentation to facilitate single particle measurements at rates
from 107 pps to 10-2 pps or lower.
Beam losses are a major concern for operation of an intensity-frontier, heavy ion accelerator. Chronic losses mustbe limited to permit maintenance with negligible impact tothe facility’s availability while fast losses must be quickly
detected and stopped to prevent severe damage. High impact loss events are typically generated by failures in the
RF systems or intercepting charge stripper devices. Slower
losses may develop from drifts in the ion source output,
slow changes to charge stripper thickness, magnet power
supplies, etc.
Lastly, a new radiation effects beamline has been built
and is currently operating on the FRIB linac [3]. This
beamline require measurement and delivery of beam fluxes
at low levels, with a minimum ~102 ions/cm2/s. This has
necessitated the development of dosimetry instrumentation.

___________________________________________* Work supported by the U.S. Department of Energy Office of Science
under Cooperative Agreement DE-SC0023633, the State of Michigan,
and Michigan State University.
† smlidia@frib.msu.edu
THXA006

THXA: Main Session THX

576

MC4.1 Beam diagnostics

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ISSN: 2226-0366

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COMMISSIONING OF LCLS-II*
A. Brachmann†, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
on behalf of the LCLS-II Collaboration
Abstract
This paper summarizes the current Status of the LCLSII after initial commissioning completed in September of2023 after achieving the formal ‘Threshold Key Performance Parameters.’ A summary of initial commissioning
was presented at the IPAC-23 conference [1]. The facility
has been delivering x-ray beams to the experimental areas
for instrument commissioning and first experiments, while
ramp-up and tuning of the accelerator and FEL continued
in parallel. Challenges encountered during this time were
malfunctioning of the Long Beam Loss Monitors (a key
safety system component), and the onset of field emission
in several cryomodules, limiting the achievable gradient.

Facility Status
The LCLS-II facility is an x-ray facility, delivering
beams based on FEL’s driven by normal (NC) and superconducting (SC) accelerators. While the NC based FEL isdelivering x-ray beams to users for more than a decade, theSC accelerator has been operating for approximately ayear. Here, we focus on the recent results achieved with thelatter. A description of the facility is given in [1]. The final
design report has more detailed information [2].
After achieving the threshold KPP’s during initial commissioning, the focus has been to optimize performance,
troubleshoot many issues, and establish routine operation,
while also providing stable x-ray beams to the experimental areas for instrument commissioning. Currently,
most of the SC beam program focuses on the soft x-ray undulators. The NC-based systems are in use almost exclusively to the user program and are delivering beams withexcellent performance.
The current status of machine performance is summarized in Table 1. A significant effort has been to continue
diagnostic development, which allowed a more efficienttuning of the accelerator and FEL systems. This included
the installation of an S-band transverse cavity (STCAV) for
longitudinal phase space characterization, energy spreadand slice emittance measurements of the injector. Furthermore, the X-band transverse cavities at the end of the undulators were upgraded with a new low-level RF and timing system that allows these diagnostics to be used withboth the NC and SC timing systems. This was enabled bya phase locking system to both fundamental accelerator
frequencies (2856 MHz for NC and 1300 MHz for SC).
Other critical diagnostics such as wire scanners and bunch
length monitors are nearly ready for routine operation.
The ramp up of the beam power is currently limited to
2kW due to safety system deficiencies described below.
___________________________________________

Table 1: LCLS-II Key Performance Parameters
Parameter
ThresholdStatusSUPER CONDUCTING BASED FEL
Beam Energy (e-)
3.5 GeV
3.8 GeV*
Repetition Rate
93 kHz93 kHzBunch Charge
0.02 nC
0.1 nCBeam Energy (ᵞ)
0.25-3.8 keV
0.2-3.8 keV
Photon # (10-3
bandwith) per
5×108@2.5 keV > 1011@3.8 keVbunch
FEL Intensity jitter
N/A
15%
Bunch charge jitter
1.5%
3%Energy jitter
1.0e-40.5e-4
Bunch length jitter
N/A4%* 93 kHz in burst mode; routine operation is 8.25 kHz
An important aspect of machine operation is beam stability. We have demonstrated stability performance that exceeds the design specifications. The critical numbers
are summarized in Table 1 and illustrated in Fig. 1.

Figure 1: SC beam stability.
Beam emittances at the injector (88 MeV) are generally
at the 0.5 µm level in both dimensions. At the end of theaccelerator, at 3.5 GeV, best projected emittances were1-1.5 µm Fig. 2 illustrates the emittance measurements forboth parts of the accelerator. The minimization of emittance degradation will be subject to further work during thecoming months.
During beam power ramp-up, we monitor the accumulated dose on the undulator segments to prevent excessive
exposure that could demagnetize the permanent magnets.
Over the last two weeks of ~2 kW beam power operation,
the first undulator cell recorded a maximum integrated
dose of ~0.08 Gy, well below the 0.2 Gy/week threshold.

* Work supported by U.S. DOE contract No. DE-AC02-76F00515† brachman@slac.stanford.edu
THZA001
582

THZA: Main Session THZ
MC2.4 FELs

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RF-BASED ENERGY SAVINGS AT THE FLASH AND
EUROPEAN XFEL LINACS
J. Branlard∗ , V. Ayvazyan, A. Bellandi, C. Christou, M. Diomede, T. Froehlich, S. Göller,
H. Schlarb, C. Schmidt, V. Vogel (Fogel), M. Vogt, N. Walker
Deutsches Elektronen-Synchrotron DESY, Germany
Abstract

Profiling the Modulator ShapeSeveral measures were developed and deployed at thepulsed linacs FLASH and European XFEL operated at
DESY in order to reduce the energy consumption of the RF
systems. A staged implementation of several techniques allowed energy savings up to 25% for both facilities, at the costof reducing the RF overhead and increasing the complexityof the low-level radio frequency (LLRF) system. However,through tool development and automation, the energy saving
linac configuration could be implemented without compromising the RF stability, maximum beam energy, accelerator
availability and with minimal impact on the setup time.

The most direct approach to reduce the power consumption is to lower the modulator HV, denoted as circle 1 inFig. 1. Both FLASH and EuXFEL have different energy
working points requiring different klystron power levels.
Changing the HV set point affects the power level where
klystron saturation occurs. One can then experimentally findthe minimum HV settings that will guarantee the maximum
klystron power required to cover typical operation scenarios,with the caveat that not all modulator voltages result in astable klystron working point. Optimizing the modulator
HV will effectively reduce the RF overhead necessary forfield regulation. Accurate resonance control using piezo andefficient field control using on-resonance cavity filling with
the LLRF system is essential to efficiently use the available
RF power [2], hence allowing for maximum HV reduction(i.e. operating just a few percent from klystron saturation).

INTRODUCTION
One third of the European X-ray Free Electron Laser (EuXFEL) accelerator energy consumption comes from generating the radio frequency (RF) fields necessary to accelerate
the electron beam. Over the last couple of years, multiple efforts to optimize the energy consumption translated
into significant energy and cost savings. A first initiative tolower the HV drive of the accelerator high-power sources(klystrons) was introduced at EuXFEL in 2022, removing theunused klystron power overhead, while preserving enoughmargin for field regulation. This first step already provided
10-15% savings [1]. As a second step, modifications of thehigh-power modulator shape combined with a more sophisticated use of the available klystron power allowed to bring thesavings up to 25%, without compromising the beam quality
necessary for photon science. A similar effort at the Free
Electron Laser in Hamburg (FLASH) was carried out, optimizing the modulator high-voltage (HV) shape with tighter
margins around the RF pulse for all accelerating stations
including the RF gun. Altogether, the RF power consumption could be reduced by 200 kW, also corresponding to a
25% saving. A conceptual description of these techniques
is presented in the first section of this report, including theirimpact on the RF and some insight on the technical solution.
The second and third sections present the energy saving
achieved at FLASH and EuXFEL, followed by a conclusion.

CONCEPTUAL DESCRIPTION
The approaches presented here to achieve energy savingby shaping the modulator HV can be applied separately or
together to combine their benefit.
∗ julien.branlard@desy.de

THZA003
584

Figure 1: Different stages of modulator HV pulse shaping(solid line): lowering the HV (1), shortening the modulator
pulse (2), introducing a step in the second half of the pulse(3). The dotted line illustrates the RF pulse scheduled during
the modulator pulse.
The next step in profiling the modulator pulse focuses on
its time duration. In the original high power settings, thewidth of the modulator HV pulse is chosen so that a stable
plateau is reached and kept for the entire duration of the
RF pulse, including some margins before and after. Somepower savings can hence be achieved by reducing, more orless aggressively the duration of the HV pulse, eating up
the margin before and after the pulse. For reference, theduration of the fill time and beam time (or flat top) are listed
in Table 1 for both facilities. This point is illustrated Fig. 1
circle 2. The reduction in pulse duration is combined with achange of trigger delays so that the savings are distributed
before and after the RF pulse. Due to the non-symmetricalshape of the modulator pulse (i.e. soft knee at the end of thefill time against an abrupt drop at the end of the pulse), theTHZA: Main Session THZ
MC4.4 Low level RF32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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H. Sakaki†, S. Kojima, T. -H. Dinh, M. Hata, T. Miyatake, M. Nishikino, T. Shirai, K. Kondo
QST, Kyoto, Japan
K. Ohtomo, H. Tsutsui, Sumitomo Heavy Industry, Tokyo, Japan
H. Kuroki, N. Inoue, Hitachi Zosen, Osaka, Japan
H. Matsumoto, Kyushu Univ., Fukuoka, Japan
S. Oishi, A. Okano, K. Ishii, Nara-Women's Univ., Nara, Japan
Abstract
A quarter of a century has passed since the discovery of
the mechanism of laser-driven ion acceleration [1, 2]. Thismechanism makes a compact ion accelerator than the present accelerators, and many applications, especially an ion
therapy, are proposed on the ion user’s studies. To develop
ion applications, it is necessary to increase the beam delivery efficiency using in the beam line adapted to the characteristics of the energetic ions transported. However, 25
years after the discovery of laser-driven ion acceleration
with ultrashort pulsed high-current ions, there are currently
no benchmark codes to simulate its transport system forapplication. We are beginning to construct a prototype oflaser-driven ion injector for benchmarking and to investigate the beam parameters in a simulation. In this report, we
describe our ongoing project "Quantum Scalpel" for heavy
ion therapy using laser-driven ion acceleration and thecommissioning of a prototype for this application.

QUANTUM SCALPEL PROJECTHIMAC in Japan, a facility dedicated to heavy particle
therapy, has been in operation since 1996. HIMAC had ahuge site area of 120 x 65 m to accelerate various heavyions other than carbon beams, which are usually used forheavy particle therapy.

Figure 2: General view of Quantum scalpel project.

Figure 1: Accelerator for advanced heavy-ion therapy inJapan.

A dedicated 60 x 45 m carbon therapy facility was developed around 2010. However, it was also too large to beinstalled in an urban area in Japan, so a downsizing project,
Quantum Scalpel [3], with novel ion acceleration technologies was started in 2016. The project was named "Quantum Scalpel" to describe the quantum-effect ion beam
those cuts through the affected area like a surgical scalpel.
The project is divided into two phases. In Phase I, an accelerator unit will be built in a newly developed 7 x 7m
superconducting synchrotron using the current high-frequency ion injector: reusing HIMAC injector.

___________________________________________† email address: sakaki.hironao@qst.go.jp
THAA: Thursday Oral Posters
MC3.2 Ion linac projects

THAA002589

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DEVELOPMENT FOR BEAM INJECTOR USING LASER-DRIVENION ACCELERATION

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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T. Torims†, A. Ratkus, G. Pikurs, Riga Technical University, Riga, Latvia
M.Vretenar, W. Wuensch, V. Bjelland, C. Garion, H. Kos, A. Cherif, CERN, Geneva, Switzerland
M. Vedani, T. Romano, Politecnico di Milano, Italy
S. Gruber, Fraunhofer IWS, Dresden, Germany
M. Pozzi, Rösler Italiana S.R.L, Concorezzo, Italy
N. Delerue, IJCLab, Orsay, France
P. Wagenblast, TRUMPF Laser und Systemtechnik GmbH, Ditzingen, Germany
Abstract
Additive manufacturing (AM) technologies, especiallypowder bed fusion, are rapidly taking their place in thetechnological arsenal of the accelerator community. A wide
range of critical accelerator components are being manufactured additively today. However, there is still much
scepticism as to whether additive manufacturing can address the stringent requirements set to complete accelerator
components. Therefore, as an advanced proof-of-principle,
a full-size, pure-copper Radio Frequency Quadrupole(RFQ) prototype was developed and additively manufactured in the frame of the I.FAST EU project. Gradually improved RFQ prototypes and related pure copper samples
manufactured by laser powder bed fusion were submitted
to a series of standard tests at CERN to demonstrate that
this novel technology and suitable post-processing can deliver the required geometrical precision, surface roughness,
voltage holding, vacuum tightness, and other relevant parameters. The results obtained are very promising andcould be of great benefit to the linac community at large.
The paper is outlining the technological developments and
RFQ design improvement process along with the obtained
results and future endeavours.

Initially, an iteration 1 prototype RFQ section was additively manufactured by Fraunhofer IWS, corresponding to
one-quarter of a 750 MHz 4-vane RFQ – see Fig. 1 [7]. To
achieve the required surface roughness parameters, threesamples were post-processed by three different surface
treatment technologies.
Table 1: Standard RFQ Requirements
Requirement
Geometrical accuracy
Surface roughness
Porosity, degassing
Peak electric field on surface
Electrical conductivity

Value
20 µm on vane tip
100 µm elsewhere
Ra < 0.4 µm for all
inner surfaces
Vacuum 10−7 mbar
~40 MV/m
90% IACSDEVELOPMENT OF RFQ BY AM
AM solutions are becoming an integral part of the accelerator community technological portfolio. A dedicated survey revealed that several challenging parts of accelerator
components already are already produced by AM, mainly
through powder bed fusion technology [1]. Nonetheless,there is still scepticism on the possibility for AM parts toattain some challenging requirements of accelerator components, i.e. surface roughness, geometrical precision, vacuum-tightness, etc [2].
The RFQ is considered as one of the most complex andarduous part and for this reason was considered as an excellent test bed for AM technologies because of its very
stringent mechanical requirements [3]. The recent development of high-frequency RFQ structures at 750 MHz [4-6]provides an excellent opportunity for AM since their reduced dimensions are compatible with modern AM machines. A summary of specific requirements for a 750 MHz
RFQ is presented in Table 1.
___________________________________________* This project has received funding from the European Union’s Horizon
2020 Research and Innovation programme under grant agreement No
101004730.
† toms.torims@rtu.lv
THAA: Thursday Oral Posters
MC3.5 RFQs

Figure 1: iteration 1 - 95 mm ¼ RFQ.
Subsequently, a complete 4-vane RFQ prototype iteration 2 was designed by RTU and manufactured by
TRUMPF. The design was optimised for AM production
and involved improved features – see Fig. 2 [8]. Based on
results obtained with iteration 1, the printed part was
treated with a two-step mass finishing process by Rösler,
aiming to address hard-to-reach areas, such as the vane tip.
Benefiting from the valuable experience gained by the
I.FAST WP10 partners [9] and excellent collaboration, an
iteration 3 of the RFQ was manufactured with a length of
390 mm, considered as an optimum to realise segmented
RFQ’s – see Fig. 3. Its design was optimised by RTU andrealised by TRUMPF [10].
THAA003
593

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DEVELOPMENT OF ADDITIVELY MANUFACTURED 750 MHZ RFQ*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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G. Eremeev, S. Cheban, S. Posen, B. Tennis, Fermi National Accelerator Laboratory, Batavia, IL, USA
G. Ciovati, M. Drury, J. Fischer, K. Macha, M. McCaughan, U. Pudasaini, A. Reilly, R. Rimmer,
M. Weaks, Thomas Jefferson National Accelerator Facility, Newport News, VA, USA
ABSTRACT
Two 1.5 GHz CEBAF C75-shape 5-cell accelerator cavities were coated with Nb3 Sn film using the vapor diffusion
technique at Fermilab and Jefferson Lab coating facilities.
Both cavities were measured at 4 K and 2 K in the vertical cavity test facility (VCTF) in each lab, then assembled
into a CEBAF quarter cryomodule at Jefferson Lab. The
cryomodule was tested at 4 K and 2 K in the CryoModule
Test Facility (CMTF) at Jefferson Lab. RF test results forboth cavities in the cryomodule are similar to those in thequalification test in VTS, with one cavity reaching Eacc =7.9 MV/m and the other - 13.3 MV/m at 4 K.

INTRODUCTION
Nb3 Sn is a promising superconductor for accelerator cavities, which has been shown to sustain magnetic fields close
to 100 mT, corresponding to accelerating gradients of about
20 MV/m [1–5]. There are several cryomodule development
projects underway that aim to exploit this superconducting RF technology for accelerator applications [6–12]. The
present contribution discusses the progress and challenges
in installing and qualifying two C75 cavities [13] coatedwith Nb3 Sn into a spare CEBAF quarter cryomodule. The
goal for this cryomodule is to be installed in the Upgraded
Injector Test Facility (UITF) at Jefferson Lab and to haveits operation tested with the beam as well as to provide theelectron beam to UITF experiments [14].

CAVITY QUALIFICATION
Two niobium 5-cell cavities, built by RI Research Instruments, GmbH, according to Jefferson Lab C75 specifications [13], were coated with Nb3 Sn coating. 5C75RI-NbSn01 cavity was made from fine grain material, and5C75-RI-004 cavity cells were made from large grain material. The cavities received the standard processing andwere tested to Eacc ≈ 29 MV/m for 5C75-RI-NbSn01 limited by the high field Q-slope, and to Eacc ≈ 19 MV/m for
5C75-RI-004 limited by multipacting-induced quench.
5C75-RI-004 was coated with Nb3 Sn at Jefferson Lab[15]. The cavity was found to be uniformly coated with amatte appearance typical for the developed multi-cell cavity
coating protocol [16].
A slow cooldown protocol was implemented during thevertical test to cool the cavity uniformly. The temperature
gradient across the cavity was maintained at about 100 mK
while cooling down through the superconducting transition
temperature. RF test results at 4 K are shown in Fig. 1. The
THAA: Thursday Oral Posters
MC4.8 Superconducting RF

cavity quality factor was about 2⋅1010 at the low fields andwas above 1⋅1010 at E𝑎𝑐𝑐 ≈ 10 MV/m at 4 K. The quality
factor was measured up to E𝑎𝑐𝑐 ≈ 13.3 MV/m before a multipacting barrier was encountered and the test was stopped.
The low-field quality factor was above 3⋅1010 at 2 K. The
quality factor exhibited a field dependence similar to that in
4 K test, but with a high quality factor.
The 5C75-RI-NbSn01 cavity received 35 µm of electropolishing in the Argonne National Laboratory facility to reset
the Nb3 Sn-coated surface for the new coating. The complete
cavity was then anodized at 30 V in a 0.1 M diluted sulfuric
acid solution as a part of the coating protocol followed at
Fermilab. The anodized cavity was coated following thecoating protocols developed for multi-cell Nb3 Sn coating at
Fermilab [17]. This was the first time a C75-shape five-cellcavity was processed and coated at these facilities.
The cavity was visually inspected and found to be uniformly coated and glossy, similar to several other cavities
coated at Fermilab. The coated surface appeared shinier thanthe one at Jefferson Lab, likely due to the thinner coating.
RF test was done at 4 K and 2 K after a slow cooldown.
The cavity quality factor was above 1⋅1010 at low fields andwas close to 1⋅1010 at E𝑎𝑐𝑐 ≈ 10 MV/m at 4 K. The maximum
gradient was limited to E𝑎𝑐𝑐 ≈ 14 MV/m by multipactinginduced quench. The quality factor was about 6⋅109 at the
maximum field. The low-field quality factor was above
4⋅1010 at 2 K. The quality factor exhibited a field dependence
similar to that in the 4 K test, but with a high quality factor.
Since both cavities met the gradient targeted for the quarter
cryomodule to be installed in the UITF, they were progressedto the pair assembly. After the pair assembly, a warm leak
was detected in the ceramic window attached to the fundamental power coupler of the 5C75-RI-004 cavity. Since thepair needed to be re-assembled, each cavity was re-tested
individually in VCTF at Jefferson Lab.
Following the disassembly from the pair, each cavity followed the typical processing steps for RF testing. It was
discovered that the 5C75-RI-004 cavity performance wasdegraded compared to the test before the pair assembly. The
low field quality factor dropped to about 1⋅1010 at low fields
at 4 K, and a sharp Q-drop was observed starting at E𝑎𝑐𝑐
≈ 3 MV/m. The cavity was limited to E𝑎𝑐𝑐 ≈ 8 MV/m, as
shown in Fig. 1. 5C75-RI-NbSn01, on the other hand, did
not show any noticeable degradation. The cavity reachedE𝑎𝑐𝑐 ≈ 20 MV/m at 2 K after multipacting processing.
After the cavities were re-tested, they were assembled
again into a pair. The assembly was evacuated, leak checked,
THAA004
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FIRST RESULTS FROM TWO Nb3 Sn CAVITIES ASSEMBLED IN A CEBAF
QUARTER CRYOMODULE

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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K. Ruisard† , A. Aleksandrov, A. Hoover, T. E. Thompson, A. Zhukov
Oak Ridge National Laboratory, Oak Ridge, TN, USA
The SNS beam test facility is a model of the SNS frontend (source through medium-energy transport). On-goingwork at the BTF focuses on accurate modeling of the beam
distribution to enable the prediction of halo losses (<100parts per million). This presentation will discuss the latest
progress towards this goal, including recent results after areconfiguration of the test beamline. Good agreement within
the 90% beam core is shown for a 30 mA beam at 2.5 MeV.

a “multi-bunch” field solver, which takes into account thefact that, due to debunching, the 402.5 MHz bunches start
to overlap in the FODO section of the beamline.
The section of lattice under study contains 10 electromagnet quadrupoles and 19 permanent magnet quadrupoles in a
FODO arrangement (108 degrees phase advance per cell).
The quadrupole focusing function is drawn in Fig. 1. The
field model consists of soft-edged, pure quadrupole fields
parameterized by magnet geometry.

INTRODUCTIONBENCHMARK CASE AT 30 mA

The aim of research at the SNS Beam Test Facility (BTF)
is to demonstrate accurate modeling of bunch evolution including space charge and early halo growth. The project uses
advanced beam phase space measurements developed at the
BTF, including a full-and-direct 6D phase space measurement and a high-dynamic-range 2D phase space measurement capable of more than 6 orders of magnitude in dynamic
range. The scope of the project is to characterize an initialbunch (1.4 meters downstream of the RFQ) at 2.5 MeV, reconstruct the distribution for simulation, and compare tomeasured output at the end of the 2.5 MeV beamline (12meters downstream of RFQ).
We show the performance of the model at 30 mA RFQ
output. This is below typical beam currents in the SNS linac.
Ongoing efforts to build a benchmark case at 50 mA include
use of a large-aperture ion source capable of higher LEBT
current. This benchmark is limited to “optimal” transport
near the matched solution for the FODO line.

Reconstruction of the input distribution is done from 3
2D phase space projections, under the assumption 𝑓6𝐷 =𝑓 (𝑥, 𝑥 ′ ) · 𝑓 (𝑦, 𝑦 ′ ) · 𝑓 (𝜙, 𝑑𝐸). Transverse phase space measurements 𝑓 (𝑥, 𝑥 ′ ) and 𝑓 (𝑦, 𝑦 ′ ) used a 2-slit system andFaraday cup. The dynamic range of this measurement islimited to 102 . The longitudinal phase space 𝑓 (𝜙, 𝑑𝐸) isdone with a dipole, vertical slit and bunch shape monitor, as
well as two vertical slits upstream of the dipole for energy
resolution. At the time of the transverse measurements, theRFQ transmitted 30 mA and for longitudinal, 32 mA.
The output distributions 𝑓𝑜𝑢𝑡 (𝑥, 𝑥 ′ ) and 𝑓𝑜𝑢𝑡 (𝑦, 𝑦 ′ ) aremeasured using the slits and Faraday cup at the end of thebeamline. No longitudinal measurement is possible at thislocation. The output distributions are characterized at 30mA from the RFQ.
Figure 2 shows the latest result from model/measurementcomparison at the end of the beamline (approximately 9.5
meters downstream of the input). The density contours areat the 79%, 32%, 10% and 1% levels. The measurement of
input phase space had a relatively low dynamic range of 102 ,although the emittance diagnostic is capable of dynamic
range in excess of 106 .
The bunch evolution between diagnostic areas is shownin Fig. 1. This plot includes data points from measured
beam profiles from 1D slit-scans measurements. The rms
calculation includes a threshold at 1% of the peak density.
The rms value is sensitive to the tail distribution, therefore
the discrepancy in rms sizes is consistent with the contour
plots in Fig. 2.

Abstract

SIMULATION MODEL PARAMETERS
The current best benchmark case uses the PyORBIT
code [1]. This case uses 200,000 macroparticles and a maximum space charge step of 1 cm to model a 30 mA beam fromthe “input” position (1.4 meters downstream of the RFQ) to
the “output” near the beamline end. The model also includes∗ This work relies on expertise and support from SNS Operations and the

Research Accelerator Division at ORNL. The US government retains andthe publisher, by accepting the article for publication, acknowledges that
the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript,
or allow others to do so, for US government purposes. DOE will provide
public access to these results of federally sponsored research in accordancewith the DOE Public Access Plan (https://www.energy.gov/doe-publicaccess-plan). This material is based upon work supported by the U.S.
Department of Energy, Office of Science, Office of High Energy Physics.
This work has been authored by UT-Battelle, LLC under Contract No.
DE-AC05-00OR22725 with the U.S. Department of Energy. This research used resources at the Spallation Neutron Source, a DOE Office of
Science User Facility operated by the Oak Ridge National Laboratory.
† ruisardkj@ornl.gov
THAA: Thursday Oral Posters
MC1.1 Beam Dynamics, beam simulations, beam transport

TRANSPORT MATRIX ELEMENTS
Measurement of lattice matrix elements allows an independent benchmark of subsections of the BTF lattice. This measurement requires scanning the coordinates of a (𝑥, 𝑥 ′ , 𝑦, 𝑦 ′ )collimated beamlet and measuring the response with a sensitive luminescent screen.
Table 1 compares the measured matrix elements to simulated values for the same optics case investigated above.
THAA005
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PROGRESS TOWARDS HALO MODELING AT
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RESEARCH AND DEVELOPMENT OF COHERENT TERAHERTZ
SOURCES AT LEBRA LINAC, NIHON UNIVERSITY*
T. Sakai†, Y. Hayakawa, K. Hayakawa, T. Tanaka, Y. Takahashi, K. Nogami
LEBRA, Nihon University, Funabashi, Japan
N. Sei, AIST, Tsukuba, Japan
Y. Sumitomo, CST, Nihon University, Funabashi, Japan
Abstract
The Laboratory for Electron Beam Research and Application (LEBRA) at Nihon University has developed freeelectron laser (FEL), parametric X-ray radiation (PXR),
and terahertz (THz) wave sources in collaboration with
KEK and the National Institute of Advanced Industrial Science and Technology (AIST) using a 100 MeV electron
linac. Each of these light sources are used for both internaland external collaborations. We are developing THz coherent edge radiation (CER), coherent transition radiation(CTR), and plane-wave coherent Cherenkov radiation(CCR) sources in the THz band for the FEL and PXR
beamlines, respectively. In particular, we are developing
THz wave sources using an artificial quartz hollow conicaltube for the CCR source and a thin aluminum plate with aspiral target surface for THz-CTR optical vortex source. So
far, we have performed parameter measurements, including beam profile and spectrum measurements, for the THzCCR and the THz-CTR vortex beams. In this paper, we describe the development and characteristics of each THz
wave source.

LEBRA LINAC AND THZ SOURCES
At LEBRA, Nihon University, we are advancing the enhancement of a 100 MeV electron linear accelerator, as illustrated in Fig. 1. Utilizing the electron beam accelerated
by this linear accelerator, we are making progress in thedevelopment of THz radiation sources within the FEL andPXR beamlines. Table 1 shows the specifications of the
LEBRA linac. In the FEL line, we are developing CER in
the THz band, which is emitted at the entrance of the bending magnet, just before the beam dump, from the electron
beam passing through the undulator within the FEL opticalresonator. The CER generated in the FEL line is intended
for applications such as bunch length evaluation and FEL
control. A transport optical system employing a perforated
mirror and an ITO mirror has been constructed to superpose and transport both the FEL and THz beams. We havesuccessfully achieved the simultaneous measurement of
FEL and THz-CER using this transport line [9-11].

INTRODUCTION
At the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University, we are engaged incollaborative research with KEK and National Institute ofAdvanced Industrial Science and Technology (AIST).
Through this collaboration, we are working to improve a
100 MeV electron linear accelerator and to develop freeelectron laser (FEL), parametric X-ray radiation (PXR),
and terahertz (THz) sources. These light sources are utilized in collaborative research both within and outside theuniversity [1-8]. The development of THz sources are being carried out in both the FEL and PXR beamlines. In the
FEL beamline, we are developing a coherent edge radiation(CER) source in the THz range. In the PXR beamline, we
are advancing the development of CER, coherent transition
radiation (CTR), planar-wave coherent Cherenkov radiation (CCR), and a CTR vortex light source. For the development of the THz CTR vortex light source, we are using
a target with a spirally shaped metal-dielectric surface as
the source. We are advancing with fundamental measurements, including beam profile and spectral analyses. In thispaper, we present the development of these various THz
sources.
___________________________________________* This work was supported by JSPS KAKENHI Grant Numbers
JP19H04406, 21K12539, 23K28360, and JKA through its promotion
funds from KEIRIN RACE.
† sakai.takeshi@nihon-u.ac.jp
THAA006
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Figure 1: LEBRA 100 MeV Linac, FEL and PXR beamlines.
Table 1: Specifications of LEBRA Linac and Light Sources
Beam Energy
RF frequency
Macropulse duration
Repetition rate
FEL wave length

40 - 1002856
5 - 202 - 101.3 - 7.5(※0.4 - 1.2)
PXR energy
5 - 47THz wavelength
0.1 - 4.0※
( Generated by a nonlinear optical crystal.)

MeV
MHz
μs
Hz
μm
keV
THz

THAA: Thursday Oral Posters
MC2.7 Synchrotron light sources

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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THE SARAF-LINAC PROJECT JULY 2024 STATUS
N. Pichoff†, A. Chance, J. Dumas, G. Ferrand, F. Gougnaud,
T. Plaisant, F. Senée, D. Simon, D. Uriot
CEA/IRFU, Gif-sur-Yvette, France
J. Luner, A. Kreisel, A. Perry, E. Reinfeld, I. Shmuely, L. Weissman
Soreq NRC (SNRC), Yavne, Israel

Abstract
SNRC and CEA collaborate to the upgrade of the
SARAF accelerator to 5 mA CW 40 MeV deuteron andproton beams (Phase 2). CEA is in charge of the design,
construction and commissioning of the linac downstream
the existing RFQ (SARAF-LINAC Project).
The MEBT is now installed at SNRC and has been commissioned with both proton (cw) and deuteron (pulsed)
beams. Transverse and longitudinal emittances have beenmeasured and beam transport has been compared with
TraceWin simulations.
Cryomodules have been assembled and tested at Saclay.
CM1 has been delivered to SNRC and is being integrated
at SNRC.
This paper presents the results of the qualification of thecryomodules at Saclay and the commissioning at Soreq.

INTRODUCTION
The last status has been presented in IPAC23 [1]. After
design (2015-2016), prototype (2017-2018), series manufacturing (2018-2022), individual qualification (20202023), critical components are now integrated into linac

subsystems (MEBT and Cryomodules) and have been
qualified at Soreq (MEBT) and Saclay (Cryomodules).
This paper presents the last results of these qualifications
tests.

MEBT COMMISSIONING
The MEBT has been delivered in August 2020, but its
commissioning has been complicated by the COVID19
travel restrictions and the co-activity in the facility. Afteran update (to EPICS) of the ECR Ion source, LEBT and
RFQ control system, the proton and deuteron beams havebeen transported to a D-plate downstream the MEBT [2].
The transmission reaches close to 100% of the RFQ accelerated particles. The results of the beam characterization
are in accordance with the simulations with TraceWIN [3].

Longitudinal Emittances Measurements
The longitudinal beam profile and emittances were
measured with a FFC through the gradient variation
method. The measured profiles were compared with theone obtained with TraceWin simulations from RFQ input
with Gaussian beam, including diagnostic transfer function
simulation (Fig. 1). The profiles fit remarkably well.

Figure 1: comparison between calculated and measured longitudinal beam profiles at FFC position.
THAA007608

THAA: Thursday Oral Posters
MC3.4 Proton linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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L. J. R. Nix∗ 1,4 , R. B. Appleby2,4 J. T. Bradbury2,4 , G. Burt1,4 , D. M. Graham2,4 ,M. T. Hibberd2,4 , S. P. Jamison3,4 , R. Letizia1,4 , C. T. Shaw2,3,4
1
School of Engineering, Lancaster University, Bailrigg, Lancaster, United Kingdom
2
Department of Physics and Astronomy & Photon Science Institute,
The University of Manchester, Manchester, United Kingdom
3
Department of Physics, Lancaster University, Bailrigg, Lancaster, United Kingdom
4
The Cockcroft Institute, Sci-Tech Daresbury, Daresbury, United Kingdom
Abstract
We have designed a tapered dielectric-lined waveguidefor the acceleration of sub-relativistic electron bunches with
THz-frequency electromagnetic pulses. We consider an
example design based on a commercial 100 keV electron
gun and a THz generation scheme driven by a mJ-level regenerative amplifier laser system. With a 12 μJ THz pulse
we simulated acceleration of a 100 keV electron bunch to
162 keV with very low energy spread. A second example
design shows energy doubling from 100 keV to 205 keV using a 22.5 μJ pulse. The former of these two designs has
been assembled for experimental testing. We also discuss
methods to improve the efficiency of the design process using 1D particle tracking to provide better estimates of theinitial geometry before optimization.

THZ-DRIVEN ACCELERATION
THz-driven acceleration has received significant researchinterest in recent years as a novel technique for compact
accelerators with fs-level bunch control [1–3]. In this work,
we study THz-driven acceleration in rectangular dielectriclined waveguides (DLWs). Such a structure consists of arectangular metal waveguide with a layer of a dielectricmaterial fitted to the top and bottom surface. This type ofstructure allows for accelerating modes with phase velocities
below 𝑐 [4, 5], and it is therefore possible for a subluminal
electron to travel in synchronism with the THz pulse in the
DLW.
The THz-driven acceleration method discussed in thiswork uses the interaction between a μJ-level THz pulse andan initially sub-relativistic electron beam. At sub-relativisticenergies, electron velocity changes significantly under acceleration. Therefore, to keep particles at the correct phase,the phase velocity 𝑣𝑝 of the pulse must start well below 𝑐
and must increase along the interaction length. The phasevelocity of a rectangular dielectric-lined waveguide (DLW)
depends on the dielectric constant 𝜖𝑟 , the thickness of the dielectric layer 𝑡𝑑 , the total waveguide width 𝑤, and the widthof the dielectric layer 𝑤𝑑 . Of these parameters, the latter
two are practical for a tapering scheme and a taper geometry
may be optimized by performing parameter sweeps acrossFigure 1: Photograph of the dielectric-lined waveguide structure and integrated coupler as assembled at STFC Rutherford
Appleton Laboratory.
the widths at several markers along the length. For manufacturing reasons, we restricted our dielectric taper to a single
linearly tapered region between two non-tapered regions,while the metal taper was allowed to be more complex. Thismethodology and the simulation results for our example
designs are presented in detail in [6].

TAPERED DLW STRUCTURE
Our accelerating structure has been manufactured by
STFC Rutherford Appleton Laboratory and will be experimentally tested in the near future.
The structure, shown in Fig. 1, will be mounted on a multiaxis alignment stage. To limit dielectric charging during
alignment, multiple channels are machined into the structure, visible as the middle and right apertures in Fig. 1. If theelectron bunch passes through the coarse alignment channel(right aperture), the whole structure can be shifted and itsalignment adjusted until the electron bunch passes throughthe fine alignment channel (middle aperture). This will
ensure minimal charging when doing final alignment adjustments for the interaction channel. Simulations on THz
coupling have shown that the power reaching the accelerating mode is negligibly affected by misalignment on theachievable scale [7], but performance is expected to be very
sensitive to electron beam alignment.

∗ l.nix@lancaster.ac.uk

THAA: Thursday Oral Posters
MC2.6 Other electron accelerators

THAA008
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THz-DRIVEN ACCELERATION OF SUB-RELATIVISTIC ELECTRONS IN
TAPERED RECTANGULAR DIELECTRIC-LINED WAVEGUIDES

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PROGRESS AND CHALLENGES IN TRAVELING-WAVE (TW)SRF CAVITY*
F. Furuta†, V. Yakovlev, T. Khabiboulline, K. McGee, S. KazakovFermi National Accelerator Laboratory, Batavia, IL, USA
R. Kostin, P. Avrakhov, Euclid Techlabs, Bolingbrook, IL, USA
Abstract

3-CELL TRAVELING WAVE CAVITY

Traveling-wave technology can push the accelerator
field gradient of niobium SRF cavity to 70MV/m or higher
beyond the fundamental limit of 50~60MV/m in StandingWave regime. The early stages of TW SRF cavity developments had been funded by several SBIR grants to Euclid
Techlabs and completed in collaboration with Fermilab
through a 1-cell prototype and a proof-of-principle 3-cell
TW cavity development and testing. The TW resonance excitation in a SRF cavity at 2K liquid helium was demonstrated as the 1st time using the TW 3-cell at Fermilab. To
advance TW technologies necessary more for future accelerator-scale TW cavity, Fermilab proposed a half-meterscale TW RF design. Here we report the recent progress inthe 3-cell and the challenges towards a half-meter scale
TW cavity.

Early Achievements
The early stages of TW SRF cavity developments havebeen funded by several SBIR grants to Euclid Techlabs(DOE SBIR Grant # DE-SC0006300) and completed incollaboration with Fermilab through a 1-cell prototype anda 3-cell proof-of-principle TW cavity fabrication andtesting. It demonstrated the feasibility of the fabricationand processing of multi-cell TW structure [4] and achieved
the TW resonance excitation in the 3-cell TW cavity atroom temperature [5, 6].

INTRODUCTION
Presently all SRF cavities operate in a standing wave(SW) resonance field in which particles experience anaccelerating force alternating from zero to peak. Niobium
SRF cavities have a theoretical peak magnetic field which
limits the accelerating field to 50 - 60 MV/m using standard available designs. A travelling wave (TW) regime
evades this limit by generating a resonance field
propagates along the cavity length. Particles in suchtraveling resonance field can experience a constantacceleration force, thus an energy gain per unit length canbe higher than that of SW regime. This phenomenon isdefied by the cavity’s transit time factor T (T=Eacc/Eave.,
Eacc - accelerating gradient including variation in time , Eave
- accelerating gradient without time dependence). A TW
structure proposed in the early study showed a T of 0.9 [1],which is >20% higher than T of most common 1.3GHz SW
9-cell design (T ~0.7). This approach explores the path to70 MV/m and higher for the same peak surface magnetic
field condition of standard Niobium materials andprocessing technology. A higher cavity quality factor withhigher R/Q of TW design can also be expected [2], which
will lower the heat load and cryogenic power. Increased
cavity energy gain per unit length and higher cavity quality
factor can dramatically reduce the scale and running costof SRF accelerators. An example, the proposed TW-based
linear collider HELEN can achieve a 250 GeV center-ofmass energy in only 7.5 km, in stark contrast to the 30-km
scale of the SW ILC structure [3].
___________________________________________*Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting
under Contract No. DE-AC02-07CH11359 with the U.S. Department ofEnergy, Office of Science, Office of High Energy Physics.
† ffuruta@fnal.gov
THAA009614

Figure 1: 1-cell prototype (left) [4] and 3-cell proof-ofprinciple TW cavity (right).

TW Resonance Control in the 3-cell Cavity
To excite TW resonance in the 3-cell cavity, the following technical concepts were investigated and demonstrated
during the early R&Ds; 1) the stiffened cavity design, 2)
RF control using two input power couplers, and 3) a special
tuner device [5, 6].
The loaded quality factor Qload at 2 K in VTS will bearound 108, making the cavity bandwidth very narrow andsensitive to microphonics. The stiffening ribs were weldedon the waveguide (WG) to reinforce the resonator (Fig. 1right). Based on the simulations, the stiffened cavity design
and fine tuning of RF input signals would be enough towithstand microphonics detuning.
The WG of the 3-cell cavity has two RF input couplers
and three RF monitoring couplers (Fig. 2). During thestudy at room temperature, a “forward” and a “backward”
traveling waves inside the cavity and WG loop were mathematically extracted from the monitoring coupler signals.
The “backward” traveling wave was suppressed by RF
power redistribution and phase control between the two input signals. With these controls and signal processing, thedesired “forward” traveling wave was successfully established in the 3-cell cavity at room temperature. Figure 3
shows RF feed and measurement scheme at room temperature for the 3-Cell TW cavity by Euclid [5].

THAA: Thursday Oral Posters
MC4.8 Superconducting RF

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DUST CONTAMINATION IN THE TRIUMF E-LINAC
A. Mahon∗ 1 , T. Junginger1 , J. Keir, P. Kolb, D. Lang, T. Planche1 TRIUMF, Vancouver, Canada
1also at University of Victoria, Victoria, Canada
Abstract
The presence of dust particulates inside the vacuum spaceof particle accelerators has been linked to a variety of issues:
At the Large Hadron Collider (LHC), beam loss events havebeen linked to the interaction of charged dust with the proton
beams. In superconducting rf cavities, dust contamination
leads to field emission, limiting the accelerating gradientand causing damage to external beamline components. Facilities such as the TRIUMF electron linear accelerator see
progressive onsets in field emission that cannot simply be
explained by vacuum events. The environment of a particle
accelerator provides an ideal opportunity for dust to gain
charge, which is one of the main drivers of dust grain dynamics in vacuum. However, fundamental parameters suchas the dust composition and charge to mass ratio of thesegrains are unique to each accelerator environment and remain largely unknown. We will present an analysis of dust
samples taken from TRIUMF linear accelerators, detailingtheir size, composition and potential sources.

INTRODUCTION
TRIUMF is undertaking a significant expansion of its
rare isotope program via the addition of the Advanced Rare
IsotopE Laboratory (ARIEL). The ARIEL facility will add
two new target stations to increase isotope production; onewill be driven by a 520 MeV proton beam from the existing cyclotron, the other by a 30 MeV electron beam froma recently commissioned superconducting electron linear
accelerator, the e-Linac (Fig. 1). The electron beam will be
used to generate high purity isotope products via photofission, a technique which yields more isotopes in the neutronrich region of the nuclear landscape [1].

Figure 1: Schematic of ARIEL e-Linac.

High Gradient Requirements
As the overall isotope production yield at ARIEL is expected to depend strongly on the electron beam energy [2],maintaining the output at – or above – 30 MeV is essential for
the ARIEL science program. Three 1.3 GHz 9-cell elliptical∗ amahon@triumf.ca

THAA010618

Figure 2: Isotope photofission yield as a function of 100kW
electron beam energy [2].
superconducting rf (SRF) cavities, made of bulk niobium,
are used to accelerate the electron beam. To reach the design specification of 30 MeV, each cavity must deliver anenergy gain of 10 MeV or higher. Figure 2 demonstrates thesteep dropoff in isotope production when the electron beamenergy, and by association the SRF accelerating gradient,
dips below this operational imperative.

Present Limitations
One practical limitation in SRF cavities is field emission [3], wherein rogue electrons are emitted from regions ofhigh surface electric field inside the cavities. Field emission
electrons cause a range of detrimental effects in accelerators.
They draw energy from the rf field, lowering the quality
factor (Q) of the resonator [4]. This increases the heat being dissipated in the cavity surface, requiring more liquid
helium consumption to maintain cryogenic temperatures atthe same gradient, ultimately forcing facilities with finite
cryo power to operate at lower gradients. Field emission
electrons may also reach relativistic velocities and generateintense bremsstrahlung and radiation damage to accelerator
components [5–7].
The TRIUMF e-Linac actively suffers from field emission,
which can be observed directly with our viewscreen diagnostics elements. Field emission electrons are accelerated
by the rf fields present in the cavities, and can consequently
travel outside of the confines of the cavity, which can thenbe picked up on our scintillator screens. An example of thisis shown in Fig. 3; in this case the field emission electrons
are escaping the confines of the adjacent cavity to reach theviewscreen further down the beamline. We are able to identify these particles as electrons, and not for example X-rays,
as we are able to steer them with the optical elements of thebeamline, proving that they are charged particles.
THAA: Thursday Oral Posters
MC4.8 Superconducting RF

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A LASER PLASMA WAKEFIELD ELECTRON ACCELERATORFOR THE ADVANCED PHOTON SOURCE AND
LOW-ENERGY ACCELERATOR FACILITY∗
K. P. Wootton† , W. J. Berg, J. Calvey, S. Chemerisov, J. Dooling, M. Edelen, V. Guarino,
C. Kozlowski, A. H. Lumpkin, V. Sajaev, F. Westferro
Argonne National Laboratory, Lemont, IL, USA
E. Aneke, Northwestern University, Evanston, IL, USA
Abstract
Recent developments in laser wakefield accelerators (LWFAs) lead us to consider employing this technology to accelerate electrons at the Advanced Photon Source (APS) facility.
Previous experiments using LWFAs were performed at Argonne using the Terawatt Ultrafast High Field Facility. The
injector complex serving the APS begins with an electron
linac, producing beam energies on the order of 450 MeV.
We consider that the infrastructure developed at the Linac
Extension Area (LEA) could be usefully employed to develop a new LWFA injector for the APS linac. In the present
work, we outline the proposed parameters of an LWFA using approximately a 100–TW–peak laser pulse focussed intoa few-mm in extent pulsed gas jet. We are targeting electron beam energies in the range 300–500 MeV. Initially, we
would use the LEA quads, diagnostics and electron spectrometer to demonstrate performance and characterize the
LWFA beam, before moving the LWFA to inject into theParticle Accumulator Ring (PAR).

INTRODUCTION
The photon beams produced by the Advanced Photon
Source Upgrade (APS-U) illuminate materials to solve themost pressing problems in science, engineering, and energy[1]. The high-power electron beams of the Low Energy
Accelerator Facility (LEAF) at Argonne are used to create
diagnostic radioisotopes for medicine [2]. As stewards ofour facilities, we endeavour to most efficiently use electricity
as we deliver needed beams.
Laser plasma wakefield accelerators (LWFAs) [3–6] arebeing developed to serve the needs of future electron accelerators, especially towards energy-frontier electron-positron
colliders and free-electron lasers [7, 8]. We propose that aneffort parallel to the high energy physics roadmap is needed
to develop this technology as an injector to a storage ringlightsource [9–11], or for production of radioisotopes using
electron beams. With an eye to material irradiation, previous work on LWFAs was performed at Argonne using theTerawatt Ultrafast High Field Facility (TUHFF) [12–14].
In the present work, we outline a a proposal to develop a
LWFA linear accelerator as for electron beam irradiation or∗ Work supported by the U.S. Department of Energy, Office of Sci-ence, Office of Basic Energy Sciences, under Contract No. DE-AC0206CH11357.
† kwootton@anl.gov
THAA012622

as an injector to the APS-U. We outline and motivate the proposal. Background and prior studies are outlined. Proposed
experimental parameters are outlined using particle-in-cellsimulations. To close, we discuss some of the potential
opportunities enabled by such a research pursuit.

MOTIVATIONA distinguishing feature of the injector accelerator chainof the Advanced Photon Source (APS) is the Particle Accumulator Ring (PAR) [15]. Situated between the electron
linac and the booster synchrotron, the PAR is used to accumulate electrons for APS electron beam operation. The large
momentum aperture of the PAR ring (∼0.1%) allows us tocapture multiple injections from an LWFA before directingthat beam on to the booster synchrotron. This approach is
not unique: a number of studies have considered matchingan LWFA to a ring [10, 11, 16–18].
Rather than attacking scientific problems associated withlarger scale facilities (such as staging multiple accelerator
segments together [19]), we propose to deploy a single acceleration stage. Specifically, we propose to develop a LWFA
based on a supersonic transverse gas jet operated in the
blowout regime, modelled along previous studies [20].
We envisage conducting this research in stages. Based on
existing demonstrations of LWFAs at other laboratories, we
propose to assembled and characterized a LWFA at the Linac
Extension Area (LEA) [21–24] to demonstrate the feasibilityof an LWFA for radioisotope production or as an injector
to the APS. We would subsequently relocate the LWFA to
inject into the Particle Accumulator Ring (PAR) [15], anddemonstrate injection into the APS-U storage ring.

BACKGROUND
Presently at Argonne, the LEAF electron linac is used
for the production of radioisotopes [2]. The linac can be
configured to provide electron beams with energies up to
50 MeV and beam powers up to 25 kW.
The injector chain of accelerators at the APS begins with
an S-band electron linac [15, 25]. The APS linac routinely
provides electron beams of energies on the order of 450 MeV.
The linac is typically operated to produce ∼1 nC of beam
charge at a linac repetition rate of up to 30 Hz (∼13 W average beam power). The APS electron linac is illustrated inFig. 1.
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PROPOSED INVESTIGATIONS OF ELECTRON-BEAM
MICROBUNCHING IN THE ADVANCED PHOTON SOURCE LINAC*
A.H. Lumpkin†, J.C. Dooling, W.J. Berg, Y. Sun, K.P. Wootton
Argonne National Laboratory, Lemont, IL, USA
Abstract
We propose extension of the investigations on the longitudinal-space-charge-impedance mechanism for inducing
microbunching of relativistic electron beams within the
Advanced Photon Source (APS) S-band linac. The microbunched content is evaluated by observing the coherent
enhancements of optical transition radiation (OTR) whensuch beam transits a vacuum-metal boundary. The facility
also uniquely includes both a thermionic cathode rf gun
and a photocathode rf gun as electron sources for comparisons of effects. In previous studies, we addressed mitigation of the COTR’s deleterious effects in the diagnostics
for the visible light 2-D beam images at 375 MeV. In thiscase we plan to elucidate the microbunching phenomenon.

INTRODUCTION
Relativistic electron beam micropulses may be compressed to a high degree producing kAs of peak current on
the sub-picosecond time scales. In addition, the charge
fluctuations may couple to the longitudinal-space-charge
impedance to generate energy modulations starting fromnoise. These energy modulations can be converted to periodic longitudinal density modulations (microbunching) ina chicane with an R56 term with gain for the initial modulation wavelength [1, 2]. If a proper beam energy chirp ispresent the longitudinal distribution will also be compressed. These interactions lead to gain at various wavelengths which can be evaluated with coherent optical transition radiation (COTR) imaging.
In previous studies, we addressed mitigation of the
COTR’s deleterious effects in the diagnostics for the visible light 2-D beam images at 375 MeV [3]. By extending
our wavelength coverage into the NIR, we will access themuch stronger enhancements predicted (>100) [1] and elucidate their spectral content. We will use an existing opticaltransport line for visible to NIR COTR (0.4 to 3.0 microns)from the diagnostics cube in the tunnel to an enclosed, external optics table. The inexpensive addition of a NIR-sensitive photodiode and integrating circuit with an existing
digital oscilloscope in the optical setup would provide immediate extension of the wavelength coverage of the detectors [4] and enable the testing of the current model predictions for the microbunching instability into the NIR.

____________________________________________* Work supported by the U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences, under Contract No. DE-AC0206CH11357.
† lumpkin@anl.gov
THPB001
626

EXPERIMENTAL FACILITY
A schematic of the linac is shown in Fig. 1 with the PC
rf gun, two TC rf guns, the S-band accelerating structures,the 4-dipole magnet chicane at 150 MeV, the mini-flag
OTR station, the subsequent 8 accelerating structures, electron spectrometer, and Station-5. Coherent Transition Radiation (CTR) monitors in L2 and L3, based on Golay cells,
detect far-infrared radiation. The THz CTR signals are
maximized at maximum compression (minimum bunch
length). Scanning one arm of the CTR interferometer provides an autocorrelation used to determine the bunch
length.

Electron Sources
The APS linac provides electron beams to the injector
complex, including the Linac Extension Area (LEA).
Three electron sources can be individually selected to deliver electron beams to the linac, in different charge configurations [5]. These include: a photocathode (PC) S-band
radiofrequency (rf) gun and two thermionic cathode (TC)rf guns. Parameters of beams from the different electron
sources are summarized in Table 1. The higher micropulse
charge of the PC gun results in stronger COTR signals.
Table 1: Parameters of Beams From he Electron Guns
Parameter
Charge per cycle
Micropulse charge
Micropulse length
Micropulses per cycle
Micropulse spacing
Repetition rate

Units
nC
nC
ps
…
ns
s-1

PC
0.3
0.3
2
1
…
6

TC
1.0
0.050
0.3
29
0.35
30

Station 5
Station-5 includes optical transport of the converter
screens’ light out to a shielded room with an optical table.
The station has three independent pneumatic actuators to
select a YAG:Ce scintillator screen plus 45° mirror, an
LSO:Ce scintillator screen plus 45° mirror, or an Al mirror
at 45° for OTR imaging. Currently there is one analog
charge-coupled device (CCD) camera for beam profilingon the optical table and the Oriel UV-visible spectrometerwith a GaAs photocathode multi-channel plate (MCP) coupled to an analog camera giving sensitivity to 880 nm. Recommissioning of these detectors could be done with TC
gun beam initially. The optical transport enables the addition of the near infrared (NIR) photodiode detector and theupgrade to a digital complementary metal-oxide semi-

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SIMULATED PERFORMANCE OF A COMPACT WATER-WINDOW FELDRIVEN BY A STRUCTURE WAKEFIELD ACCELERATOR∗
R. A. Margraf-O’Neal† , P. Piot, J. Power, J. Xu, Argonne National Laboratory, Lemont, IL, USA
Abstract
Free-electron lasers (FELs) send an accelerated electron
beam through a magnetic undulator to provide a source ofcontinuously tunable, short (10s of fs), high-peak power(GW-scale) radiation. FELs have found many applications,particularly in the infrared, extreme ultraviolet (EUV) and
X-ray regimes. However, current EUV and X-ray FELs
are large (100s of m) and expensive facilities, limiting theaccessibility of these sources. In this work, we present FEL
simulations driven by a compact accelerator combining highgradient short pulse two-beam wakefield accelerators andshort-period superconducting undulators. An FEL demo
based on a GeV-scale accelerator is discussed as a driver
for a water-window (2.3–4.4 nm) FEL with a ∼50 m length.
Such a proof-of-principle integrated facility would serve thedual purpose of supporting user-based research in the waterwindow regime, and providing a proving ground for these
new technologies to later be applied to shorter wavelength
FELs. Here, we present early design and simulation efforts
with a focus on FEL-process modeling.

INTRODUCTION
In the pursuit of high-gradient accelerators for future highenergy particle physics colliders, several technologies, including structure wakefield acceleration (SWFA), plasma
wakefield acceleration (PWFA), and laser wakefield acceleration (LWFA) are now nearing sufficient maturity for commissioning of intermediate-energy (∼1 GeV scale) demonstrator facilities. Compact free-electron lasers (FELs), which
use electron beams to produce an energy-tunable source ofhigh intensity radiation, are a logical application of such
facilities. When combined with short-period undulators [1],single GeV-scale electron beams can produce photons in
the EUV and soft X-ray. FEL demonstrator facilities havealready been proposed for PWFA in this regime [2, 3], andfor LWFA at slightly longer wavelengths [4]. In this work,
we describe the radiation stage of a ”water window” FEL
facility utilizing a two-beam, short pulse SWFA [5].
The wavelength range of 2.3–4.4 nm (280–540 eV) is
often referred to as the ”water window,” so named forthe transparency of oxygen (and thus water) to soft Xrays in this range. This regime is particularly useful tothe study of organic molecules, containing the absorption
K-edges [6] of both carbon (4.37 nm/284 eV) and nitrogen (3.09 nm/402 eV). Additionally, the oxygen K-edge(2.33 nm/532 eV) sits on the high-energy boundary of the∗ This research is based on work supported by Laboratory Directed Re-

search and Development (LDRD) funding from Argonne National Laboratory, provided by the Director, Office of Science, of the U.S. DOE
under Contract No. DE-AC02-06CH11357.
† rmargrafoneal@anl.gov
THPB005630

water window, enabling the characterization of oxygencontaining molecules with high absorption when transparency to water is not required. Common experimental
uses of the water window include soft X-ray microscopy [7],where transparency to water increases the feasibility of measuring thick aqueous samples, and spectroscopy [8], particularly of organic molecules.
High harmonic generation (HHG) sources can provide lowpulse intensity soft X-ray pulses with a table-top scale facility
footprint [7, 9, 10]. However, electron beam-based sources,
such as electron storage rings and free-electron lasers (FELs),
can provide significantly higher pulse intensity, at the cost ofa typically much larger and more expensive facility [8, 11].
The potential of high-gradient accelerators to reduce the sizeof these facilities could significantly reduce cost, making
water window pulses accessible to a larger number of users.

GENERAL FACILITY PARAMETERS
The SWFA method under development at Argonne,
known as short-pulse two-beam acceleration (TBA), uses adrive beam to generate short RF pulses that allow the accelerating structure to operate at a high acceleration gradient. The
wakefield radiation (typically X-band) is produced as a highcharge drive bunch train travels in a decelerating structure,and is extracted and transferred to a separate high-gradientaccelerating structure. Due to the beam-produced X-band
pulses being much shorter (𝜏𝑅𝐹 ≤10 ns) than conventional
klystron-produced X-band pulses, and the electrical breakdown scaling as 𝐵𝐷𝑅 ∝ 𝐸030 𝜏5𝑅𝐹 , the secondary structure
can sustain high electric field (𝐸0 ) amplitudes. This is the
key to achieving high acceleration gradients with a TBA
accelerator.
The proposed facility, diagrammed in Fig. 1, utilizes a
400 MV/m 11.7 GHz X-band accelerating gun (describedin [5, 12, 13]), followed by a 250 MV/m X-band linac, bothdriven by beam-generated X-band radiation. The X-band
linac would follow the same principles of the X-band accelerating gun, and would be designed as a part of this facility’s
development. A subsequent 26 GHz K-band, 150 mV/mlinac (”LK1”) linearizes the longitudinal phase space before
compression in a chicane (”BC1”). The beam then undergoes an additional stage of acceleration and compression in
LK2 and BC2, followed by a final acceleration stage in LK3.
LK2 and LK3 are assumed to also be 11.7 GHz, 250 MV/m
linacs, but could be replaced by K-band linacs to reducecomplexity at the cost of additional length. A dechirper isused to reduce the correlated energy spread before the final
beam is sent into the undulator to produce soft X-rays.
THPB: Thursday Poster Session
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32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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NB3SN TECHNOLOGY FOR LOW-BETA LINACS*
T. Petersen†, M.P. Kelly, T. Reid, Y. Zhou, B. Guilfoyle
Argonne National Laboratory, Lemont, IL, USA
G. Eremeev, S. Posen, B. Tennis, Fermi National Accelerator Laboratory, Batavia, IL, USA
S. Kutsaev, R. Agustsson, E. Spranza, RadiaBeam, Santa Monica, CA, USA
Abstract
Nb3Sn is the most advanced potential successor for niobium in superconducting RF accelerator cavities. Nb3Sn
has a significantly higher critical temperature (18.3 K)
compared to that of niobium (9.2 K). This has a large effecton the BCS surface resistance, and therefore, on the dynamic RF losses at 4.5 K. The higher critical temperatureallows two important changes for cavity and cryomodule
design. First, the lower BCS losses allow the designer to
use a higher frequency, translating to physically smaller
cavities and cryomodules. Second, the low dynamic losses
allow the use of stand-alone cryocoolers instead of complex helium refrigerators and distribution systems. Fabrication of a prototype 218 MHz cavity, test results, and continuing challenges are discussed.

INTRODUCTION
Heavy-ion linear accelerator resonators based on niobium are necessarily designed around for relatively low
frequencies to keep the BCS resistance manageable for operation. This BCS resistance is the main source of surface
resistance for niobium cavities and is strongly dependent
on frequency and operating temperature. Figure 1 gives acomparison of calculated BCS resistance for niobium (attwo frequencies, 72 MHz and 218 MHz) and for Nb3Sn (at218 MHz). At the operating temperature of 4.5 K the advantage of lower frequencies for bare niobium is clear.
However, Nb3Sn, even at the higher frequency, offer the
possibility of an order of magnitude lower BCS resistance.
The higher frequency translates to physically smaller cavities (reducing raw material costs as well as cryomodule
fabrication size and cost) and a much lower dynamic RF
load allowing the utilization of cryocoolers.
With the substantially higher Tc, Nb3Sn could allow
low-beta cavity operation at frequencies up near 1 GHzwith a few nΩ of surface resistance [1].

PROTOTYPE FABRICATION
A prototype quarter wave cavity was constructed withhigh purity (RRR>250) niobium (and reactor grade for all
non-RF surfaces) to serve as a base for the thin Nb3Sn coating. The frequency chosen was 218 MHz, a harmonic of*This material is based upon work supported by the U.S. Department ofEnergy, Office of Science, Office of Nuclear Physics, under contract number DE-AC02-06CH11357, and the Office of High Energy Physics, undercontract number DE-AC02-76CH03000. This research used resources of
ANL’s ATLAS facility, which is a DOE Office of Science User Facility†tpetersen@anl.gov

THPB006
634

Figure 1: SRIMP calculated BCS surface resistance of Nb(at 72 MHz and 218 MHz) and Nb3Sn (at 218 MHz) vsoperating temperature.
the ATLAS clock, and substantially higher than typicalquarter wave cavities. Subassemblies were hydroformed at
a local shop, Stuecklen Inc. The complex center conductor
tip and gussets were machined by our collaborators at RadiaBeam. All welds were performed by electron beam
welding at Sciaky Inc. The finished cavity was electropolished (125 μm) before cold testing without low temperature baking (Fig. 2).

Figure 2: Cavity being inserted into 24” dewar (left) andsection view of the cavity test assembly (right).
Following fabrication, the bare niobium cavity was coldtested to verify a good substrate for the thin film coating.
The intent was to identify any possible defects that could
cause early quench in the coated cavity testing. The cavity
had a low Q of 8 × 108, but this was expected as the cavity
was not de-gassed and showed classic symptoms of Q-disease. However, the cavity met the design goal of 60 mT
peak magnetic field, no defect initiated quench.
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32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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PROGRESS UPDATE ON THE RF SYSTEM REFURBISHMENT
AT THE APS LINAC∗
Y. Yang† , N. DiMonte, G. Fystro, D. Meyer, A. Nassiri, T. Smith, Y. Sun, S. G. Wang
Advanced Photon Source, Argonne National Lab, Lemont, IL, USA
RF STATION DEVELOPMENT

Abstract
A new storage ring, which utilizes a multi-bend achromat(MBA) lattice, has been built at the Advanced Photon Source.
Currently, the commissioning process is ongoing in order tobring beamlines back into operation. The APS linac consistsof two S-band thermionic cathode guns, one photo-cathodegun at the front end, and thirteen S-band traveling-wave
RF structures, all powered by five klystrons. A significant
refurbishment is underway to upgrade the RF system in
the APS linac. This includes the replacement of the highpower modulators and klystrons with a newly designed solidstate switching modulator RF system. In addition, the RF
control and diagnostic systems are being upgraded to thenew digital LLRF systems. To date, one RF station has
been successfully replaced, commissioned, and has been in
operation for almost two years. The RF stability, and power
efficiency at this station is notably improved compared tothe other stations.

INTRODUCTION
The Advanced Photon Source has been successfully upgraded after a year-long shutdown. The original storage
ring has been replaced with a new ring using a multi-bend
achromat (MBA) lattice. The new storage ring has beensuccessfully commissioned. We are currently in the processof bringing each of the 71 beamlines around the ring into
operation [1]. The upgraded X-ray, generated by the newstorage ring will be up to 500 times brighter.
The APS linac needs to operate between 400 MeV and 500
MeV with high reliability for the new machine [2]. The linac
setup is shown in Fig. 1. The electron beam is generated by
one of two thermionic cathode guns (RG1 and RG2) andaccelerated by three sectors of S-band traveling wave RF
structures (L2, L4, and L5). Each sector consists of four
linac structures powered by a klystron and a SLED power
compressor. Currently, the APS linac has five operating
RF stations (K1 through K5). K6 is used as a SLED test
stand [3]. Each station uses a pulse-forming network (PFN)
type pulse modulator to supply power to a Thales-35/45
MW klystron [4]. The original LLRF systems for the APS
linac have been in operation for around 30 years, and it’schallenging to find spare components and replace them whenneeded.
∗ Work supported by U.S. Department of Energy, Office of Science, Officeof Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

† yaweiyang@anl.gov

A new RF station has been developed for the APS linac. It
includes a Cannon S-band klystron, a Scandinova solid-state
modulator, and a Libera LLRF system.

Solid State Modulator and KlystronThe solid-state pulsed power modulator technology has
been implemented globally to replace conventional klystron
modulators. In contrast to a PFN-type modulator, whichuses a thyratron tube as the high-power switch, a solid-state
pulse modulator uses semiconductor switches such as the
Insulated Gate Bipolar Transistor (IGBT). Each IGBT ispowered by a DC power supply. A pulse transformer steps
up the voltages from the IGBT to the high power level for the
klystron. This technology offers significant improvements
in power efficiency, compact footprint, pulse flatness andDC stability for RF stations used in accelerators [5].
We have selected the K400 solid-state modulator, developed by Scandinova Systems, for the new RF station. The
modulator consists of two Capacitor Charging Power Supply(CCPS) units and twelve IGBT switch units. Each CCPS
unit converts a three-phase AC power line to DC voltage,
which charges six IGBT units to a primary voltage of around
1 kV. An external trigger gates the charged IGBT switches
to discharge, generating a high-power pulse of around 350
kV through the pulse transformer. This high-power pulse
is capable of powering an S-band klystron to generate RF
pulses with a peak power up to 60 MW and 4.5-µs width.
The APS linac currently utilizes Thales TH2128 klystrons,
capable of generating a peak power of 35 MW. However, it
is incompatible with the K400 modulator. Therefore, theCanon (Sumitomo) E3712 klystron was chosen as the new
klystron to work with the new modulator.
To conduct the site acceptance test, a dedicated utility
shed was developed. The first system was delivered to ANL
in 2021, and a comprehensive site test was carried out in theshed. Figure 2 shows the first installed system in the utility
shed. During the test, we collaborated closely with the vendor to resolve the identified issues and developed operationand maintenance procedures. Eventually, the klystron output
power reached 60 MW during the test.

Digital LLRF System
A customized digital LLRF system has been developed by
Instrumentation Technologies to control the APS linac RF
station [6]. This system has 22 RF monitor inputs, with each
input capable of providing amplitude and phase waveforms
with 8 ns resolution. A customized LLRF software has beendeveloped to extract average and peak information from

THPB007

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638

MC2.7 Synchrotron light sources

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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N. Bazin†, S. Berry, R. Cubizolles, G. Devanz, H. Jenhani, C. Simon, Université Paris-Saclay, CEA,
Département des Accélérateurs, de la Cryogénie et du Magnétisme, Gif-sur-Yvette, France
Abstract
The Proton Improvement Plan II (PIP-II) project at Fermilab is the first U.S. accelerator project that will have significant contributions from international partners [1]. CEA
joined the international collaboration in 2018, and will deliver 10 low-beta cryomodules as In-Kind Contributions to
the PIP-II project, with cavities supplied by LASA-INFN(Italy) and VECC-DAE (India), and power couplers andtuning systems supplied by Fermilab. An important milestone was reached in April 2023 with the Final Design Review of the cryomodule, launching the pre-production
phase. This paper presents the status of CEA activities on
the construction of the LB650 pre-production cryomoduleand the upgrade of the existing assembly and test infrastructures to the PIP-II requirements.

INTRODUCTION
The PIP-II project is an upgrade of the accelerator complex of Fermilab [2] to enable the world's most intense neutrino beam for the Deep-Underground Neutrino Experiment (DUNE) housed in the Long Baseline Neutrino Facility (LBNF) located in South Dakota, 1200 km from theneutrino production in Illinois.
PIP-II will deliver 1.2 MW of proton beam power fromthe injector, upgradeable to multi-MW capability. The central element of PIP-II is an 800 MeV linear accelerator,
which comprises a room temperature front end followed bya superconducting section. The superconducting section
consists of five different types of cavities and cryomodules,
including Half Wave Resonators (HWR), Single Spoke andelliptical resonators operating at state-of-the-art parameters.

OVERVIEW OF THE CEACONTRIBUTION TO THE
PIP-II PROJECT
Thanks to the expertise in designing, building, testing,installing, and commissioning superconducting linear accelerators, CEA joined the PIP-II collaboration in 2018.
The involvement of CEA in the PIP-II Linac construction
was formally approved by the French Ministry of Researchin July 2020 with the definition of the scope of work andthe budget envelope.
CEA contribution focuses on the 650 MHz superconducting accelerating section, with the design, fabrication,assembly, and test of 1 pre-production and 9 production

low-beta 650 MHz cryomodules (called “LB650” hereafter) according to the PIP-II project specified requirements.
This includes:• The design of the LB650 cryomodule.
• The procurement of most of the components of the cryostat (i.e. the cryomodule without the cavities, the tuning systems, the power couplers and some standard
components provided by the PIP-II collaboration).
• The assembly and cold RF tests of the 10 LB650 cryomodules.
• The design of the transport frame for the LB650 cryomodules, fabrication of 3 units, and road test of the
pre-production cryomodule.
• The preparation for overseas shipment to the USA before the transfer title from CEA to the U.S Departmentof Energy (DOE).

DESIGN OF THE LB650 CRYOMODULE
The LB650 cryomodule houses four 5-cell β=0.61 cavities (developed by Fermilab, INFN [3], and VECC for the
pre-production cryomodule and series cryomodules). The
frequency tuning systems and the power couplers for the
low beta and high beta cavities are identical. They are under the responsibility of Fermilab, with CEA contribution
on the design studies of the power couplers. Each cavity isconnected to a supporting system that stays at room temperature, called the strongback, using two support posts
made of low thermal conductivity material to limit the thermal load between the room temperature strongback and thehelium temperature devices.
The LB650 cryomodule is like the HB650 prototype cryomodule that was qualified at Fermilab [4, 5]. To benefit
from the efforts in the HB650 cryomodule design to be applied to the LB650 one, CEA was part of the integrated design team with Fermilab, UKRI-STFC, and DAE, and wasin charge of the mechanical and thermal design of thestrongback of the HB650 prototype cryomodule and thedesign of the endcap tooling (based on the one used for theassembly of the ESS cryomodules at CEA).
Lessons learnt from the assembly and tests of the HB650
prototype cryomodule have been implemented in the design of the LB650 cryomodule. This one was independently reviewed in April 2023. The Final Design Review, which is an important milestone for the CEA activities, marks the end of the design phase and opens the construction phase of the LB650 pre-production cryomodule.
The design of the LB650 cryomodule is described in [6].
Figure 1 presents an artist view of this cryomodule.

___________________________________________† nicolas.bazin@cea.fr

THPB: Thursday Poster Session
MC3.4 Proton linac projects

THPB010641

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STATUS OF THE CEA CONTRIBUTION TO THE
PIP-II LINEAR ACCELERATOR

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB011

S. Berry†, A. Bouygues, J. Drant, A. Gonzalez-Moreau, C. Servouin, C. Madec, A. Madur
Université Paris-Saclay, CEA, Département des Accélérateurs,de la Cryogénie et du Magnétisme, Gif-sur-Yvette, France
Abstract
The assembly of cavity string in the clean room is a tedious work that has noisy and painful steps such as cleaning the taped holes of a part. CEA together with the company INGELIANCE has developed a cobot: a collaborative
robot operated by a technician one time and repeating theaction without the operator. The cobot can work anytime
without any operator: Therefore, it is working at night reducing the assembly duration by several hours. The cobot
consists of a FANUC CRX-10iA a 6-axis arm on an Arvis
cart. At CEA, the cobot is used to blow the flange of thecavities and the bellows inside. This allows to reduce thenoisy steps that the technicians are exposed to. The process
is also more reproducible since the cobot does always thesame steps. The cobot is used on ESS cavity string assembly to clean flanges but also beam vacuum surface as intercavity bellows. Our activities, results and technical choices
for next development will be presented in this article.

INTRODUCTION
Laboratories beyond CEA [1] are advancing robotizationand cobotization for clean room operations. MSU in the
USA has developed a robotized high-pressure rinsing system that enhances the cleaning process by adjusting to thecavity's geometry [2]. KEK in Japan is developing a systemfor cleaning cavities and assembling components [3]. Cavity string assembly in the clean room is a tedious work thathas noisy and painful steps such as cleaning the taped holesof a part. It is recognized that humans are the biggest sourceof particulate contamination during assembly operations
on sensitive components in cleanrooms.
A COllaborative roBOT (hereafter cobot) can work anytime with or without operators including overnight, reducing painful work and assembly duration by several hours.
The use of cobot is also motivated by the fact that cavity
string components are well defined, immobile and the assembly phase remains identical during the production.
The repeatability is an issue for operators, whereas it is
an important advantage and objective for a cobot. The quality of cleanroom operations could be improved by limiting
the inherent variability of human operators.

CEA OBJECTIVES FOR COBOTISATION
CEA’s final objective is the assembly of cavity strings
with a cobot. This objective contains two sub-efforts:
cleaning and assembly of components (the latter being themost difficult). CEA initially cleaned parts under blowing___________________________________________† stephane.berry@cea.fr.

THPB: Thursday Poster Session
MC4.2 Cryomodules and cryogenics

nitrogen. However, assembling with the vacuum surfaces
exposed to the cleanroom environment has more impact on
the quality (i.e. cavity specifications) and is now being addressed as a priority. The cleaning of parts with the cobot
have been reported for ESS cryomodules assembly [4].
All the development presented hereafter required several
steps of modeling and programming. The cobot used at
CEA comes from FANUC and the programs are realizedwith Roboguide. The preparatory work consists of path
programming, vision-based localization of parts, then the
cobot will adapt the recorded paths. All cobot actions canbe prepared in advance. The small change in our strategy
since ESS experience is the introduction of the tool changer
in order to be able to clean parts which requires different
End-of-Arm tools (EOAT) or to insert intermediate cleaning steps during assembly. The tool changer is from WINGMAN company, electrical and compress air Pass-throughinterface depends on the need of the EOAT.

CLEANING OF COMPONENTS
The first step is the cleaning of following component:
 Environment of cavities,
 Flanges and their holes,
 Gasket groove in between flanges,
 Inter-cavity bellows (most critical parts at last).
The cleaning is performed going from the dirtier part tothe cleaner such as environment of cavities, then flanges
and their holes, then the cavity-to-cavity bellows (as shownin Fig. 1). Operators always install the objects to becleaned and remove the screws and studs from the flanges
to be cleaned. The cleaning is realized by blowing ionized
and filtered air (6.5 bar). The cleaning efficiency is validated by particle counting performed by the cobot monitoring a particle air borne counter (28,3L per flange’s hole).
The cleaning of components is implemented since May
2022 in ESS project with a CRX-10iA. Up to now, it has
been used for 17 cryomodules preparation (24 cryomodules delivered). Cobot and operators can work independently in parallel or cobot works at night, it’s a timesaver for ESS string assembly in the clean room: ~1/4 ofassembly time. Cleaning is very efficient and meets perfectly ESS cleaning specifications.
Table 1 summarizes the statistics of the last particle
counting performed by the cobot for the 17 ESS cryomodules assembled up to now. About 68 flanges of each type
(coupler flanges, beam flanges with right angles valve andbeam port with blind flanges) are taken into consideration.
THPB011645

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COBOTISATION FOR SRF CRYOMODULES AT CEA:
FOCUS ON ESS AND FUTURE PROSPECTS

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

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STATUS OF THE TEST BENCH FOR THE PIP-II LB650
CRYOMODULES AT CEA
H. Jenhani†, C. Arcambal, N. Bazin, Q. Bertrand, P. Bredy, G. Devanz, L. Maurice, O. Piquet,
P. Sahuquet, C. Simon, Université Paris-Saclay, CEA, IRFU, Gif-sur-Yvette, France
Abstract
The Proton Improvement Plan II (PIP-II) project at Fermilab is the first U.S. accelerator project that will have significant in-kind contributions (IKC) from international
partners. As a part of the French IKC to this project, CEA
will provide ten 650 MHz low-beta cryomodules (LB650)
equipped with cavities from INFN-LASA (Italy), Fermilab(USA), and DAE-VECC (India), and power couplers andRF tuning systems from Fermilab. CEA is in charge of thedesign, manufacturing, assembly, and testing of these cryomodules. This paper presents the progress of the future
implementation of the test stand dedicated to the cryogenic
and RF power testing of the LB650 cryomodules.

INTRODUCTION
The central element of PIP-II is an 800 MeV linear accelerator that will deliver 1.2 MW of proton beam powerfrom the main injector [1]. The CEA major contribution isthe design [2], fabrication, assembly [3], and testing of ten
LB650 cryomodules. An overview of the CEA contribution
to the PIP-II project is given in references [4].
The construction of a new test bench dedicated to testing
the LB650 cryomodules at the Saclay test facility Supratech Cryo/HF [5] represents one of the most significant
activities within the CEA scope [4]. Each LB650 cryomodule will undergo comprehensive cryogenic and RF testingat CEA to evaluate its performance against a defined Acceptance Criteria List (ACL) [6]. Several important procurements have been initiated to meet the requirements ofthese cryomodule validation tests. An overview of the main

procurements and the related key technical requirements is
also detailed in the aforementioned reference.
This paper provides an updated overview of CEA’s activities related to the procurement of new cryogenic equipment and the associated distribution network, the establishment of the new RF power facility, and the upgrade of thecryomodule test cave previously used for the qualification
tests of height ESS cryomodules with elliptical cavities andfour SARAF cryomodules with HWR cavities.

CRYOMODULE TEST BENCH
The preparation of the LB650 cryomodule test bench iswell advanced. The exact position of the cryomodule has
now been finalized (see Fig. 1). This has enabled the completion of the Secondary Cryogenic Transfer Line (SCLT)
and RF waveguide path definitions, as well as provided essential input for radiation calculations. These calculations
are based on various cavity test configurations, particularly
the maximum accelerating gradient tests and the multi-cavity nominal accelerating gradient tests, both conducted incontinuous wave (CW) mode.
For a better understanding of the choices explained inthis paper, it is highly recommended to see the details giving in [6] about the LB650 Cryomodule design, validation
tests and main procurements technical requirements.

MAIN CRYOGENIC EQUIPMENTPROCUREMENTS
The main procurements for the cryogenic equipment are
the cryogenic transfer lines, the valve box and the cold box.

Figure 1: LB650 cryomodule test bench at CEA-Saclay.
THPB012648

THPB: Thursday Poster Session
MC4.2 Cryomodules and cryogenics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA

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ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB014

INTRABEAM SCATTERING SIMULATION WITH A NOVELHYBRID-KINETIC MONTE CARLO METHOD FOR
LINEAR ACCELERATORS
P. Desiré ∗ , 1 , A. Latina, CERN, Geneva, Switzerland
A. Gerbershagen, University of Groningen, Groningen, Netherlands
1also at University of Groningen, Groningen, Netherlands
Abstract
Recent studies have identified intrabeam scattering (IBS)
as one of the processes that can have a significant impact
on the beam dynamics of linacs with high-density and lowenergy beams, such as in free electron sources (FELs), where
IBS appears to be one of the effects that most limits theirperformance. Most existing simulation codes have beendeveloped for circular lattices or assume Gaussian beams
and thus cannot accurately simulate the desired scenario.
Motivated by this problem, this work presents the implementation of IBS in RF-Track, a tracking code developed
for linear accelerators. The numerical simulation follows anovel methodology based on a hybrid-kinetic Monte Carloapproach. The method has proven to be stable using different input parameters and has shown emittance and a SlicedEnergy-Spread (SES) growth in different scenarios, demonstrating the accuracy of the tool and making it a promisingsolution to understand SES growth in FELs.

INTRODUCTION
Intrabeam Scattering (IBS), which consists of particle-toparticle elastic collisions by Coulomb interaction, has been
extensively studied due to its critical role in the performanceof circular accelerators. IBS causes emittance growth instorage rings [1] and damping rings [2, 3], leading to a deterioration of their performance. Lately, it has also beenshown to limit the efficiency of linear accelerators.
The latest photoinjector technologies have allowed freeelectron laser light sources (FELs) to have much more dense
beams, increasing the effect of IBS, which grows for lowenergy and high-density beams. In fact, recent studies haveshown that IBS can be a determining factor in the performance of these machines, as it causes a growth in the SlicedEnergy Spread (SES, also known as uncorrelated energy
spread), which is a key parameter for efficient light production. SwissFEL obtained a SES of 15 keV with 200 pC
bunches [4], whereas European XFEL found a value of 6 keVwith 250 pC bunches [5]. Finally, the PhotoInjector Test facility at DESY Zeuthen, also for 250 pC bunches, measured
2 keV [6]. The mentioned results highly differ from the SESof around 1 keV predicted from simulations, which did notconsider either Micro-Bunching Instabilities or IBS effects.
For a better understanding of this problem, a simulationaccounting for IBS is needed.
∗ pdesirev@cern.ch

THPB014652

Most of the existing simulations are based on analyticaldescriptions of IBS, such as Piwinski’s [7] or Bjorken andMtingwa [8] formulations which assume Gaussian beams,
an unrealistic approximation for the high-intensity and lowenergy beams present in many linear accelerators. Some
codes model the IBS effect based on a partial differential
equation that describes the system evolution [2], but in thiswork, each collision is reproduced individually with a Monte
Carlo (MC) method, aiming to maximize the accuracy. Thisidea has been exploited by the tracking codes MOCAC [9]and SIRE [10–12] for circular lattices and recently has beenstudied in linear architectures [13]. Our work builds on thisidea, introducing a novel methodology: a hybrid-kinetic MC
approach.
In this paper, the implementation of IBS in RF-Track [14],a tracking code developed for linear accelerators, is presented. The IBS effect was analyzed in two different proposed cases which showed the emittance and SES growth
respectively. Both scenarios used different input simulation parameters to test the stability and convergence of themethod.

IMPLEMENTATIONThis section describes the logic followed by the proposed
IBS algorithm, which follows a novel approach different
from other Monte-Carlo-based implementations. Firstly, it
is named “kinetic” because it calculates the force experienced by each macro particle in the bunch at each time step(𝑑𝑡) and applies it in the form of a thin kick. This is thestandard approach used in RF-Track to compute and apply
collective effects to the beam. Secondly, it is described as“hybrid” because the deflecting force is computed colliding
each particle with an average particle obtained from a set of
3D meshes containing charge density, velocity, and temperature of the bunch in the 3D space. In particular, three 3D
meshes are needed: one for the average velocity, one for the
standard deviation of the velocity, and one for the charged
density. Finally, the deflection angles are computed using
an MC method where the Rutherford cross-section is used
to resolve the kinematics of the interaction.
After creating the described 3D meshes, the algorithm
iterates over all the particles in the bunch, applying the following three steps. The 3D meshes are updated at each IBS
calculation.
THPB: Thursday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB015

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VALIDATION OF HIGH EFFICIENCY KLYSTRON TECHNOLOGY
P. Alonso-Arias∗ , N. Catalán-Lasheras, A. Chauchet, S. González-Antón, C. Marrelli,
I. Syratchev, Z. Un-Nisa, M. Webber, CERN, Geneva, Switzerland
M. D. Jones, ASTec STFC Daresbury Laboratory and Cockcroft Institute,
Sci-Tech Daresbury, Warrington, U.K.
M. Boronat, IFIC (UV-CSIC), Valencia, Spain
T. Anno, Canon ETD, Otawara, Japan
Abstract
The delivery of high RF power—from hundreds of kW
to MW—by klystrons, is linked with a high overall energy
consumption. A research programme led by CERN in collaboration with the industry is being conducted to understandwhat limits klystron efficiency and how to develop highefficiency klystrons. As a result of this program, two first
prototypes of X-band (11.994 GHz) high-efficiency klystrons
have been successfully designed and manufactured in collaboration with Canon Electron Tubes and Devices. The first
results look promising, revealing a remarkable 56 % efficiency, and validating the proposed HE klystron technology.
A comprehensive characterisation campaign has been conducted at CERN to verify and demonstrate these results. The
methodology for the HEK tubes characterisation is based in
two independent measurements: a RF power measurement,
and a calorimetric methodology—less subject to calibration inaccuracies. We describe the setups, principle of thecalorimetry methodology, and we discuss the feasibility andprecision of the results.

INTRODUCTION: AN X-BAND
HIGH-EFFICIENCY KLYSTRON

Figure 1: Expected performance of the E37117 tube (HEX8)
built by CANON ETD in collaboration with CERN in comparison with the original model E37113.
The new high efficiency tube E37117 uses a retrofit approach from the original Canon E37113 model. The originalmodel, used for years at CERN Xboxes facilities, delivereda maximum power of 6 MW for a 5 s pulse and 400 Hz repetition rate. Canon ETD delivered two new prototypes fol∗ paz.alonso.arias@cern.ch

THPB015656

lowing the design provided by CERN, which maintained theelectron gun and the collector, and introduced a six-cavity
bunching circuit followed by a three-cell output cavity [1].
In addition, the tubes include a new ceramic window presenting lower surface electrical fields—result of a previous
collaboration between CERN and Canon ETD—, which allows higher peak powers. In Fig. 1 and Table 1, we present
the expected performance of the new klystrons in comparison with the original model.
Table 1: Performance Metrics of the X-band Klystron Tubes
Manufactured by Canon ETD for CERN
Beam voltage, kV
Beam current, A
Peak output power, MW
Efficiency

E37113

E37117

157
96
6
39

153
93
8
56

TEST STAND FOR X-BAND HEK AT CERN
The two prototypes have been installed for their testingin the Xbox3 klystron-modulator system at CERN. Xbox3
is used to evaluate and test high-gradient accelerating structures and high-power RF components in the context of theCompact Linear Collider (CLIC) project [2].
The system consists of a Scandinova 170 kV modulator
system that delivers the pulsed power to the klystron cathode, waveguide network for the distribution of the RF power,
pulse compressor, and auxiliary power supplies and dedicated subsystems for control, interlocking, and diagnosis.
Originally, Xbox3 was designed for conditioning structures
rather than testing klystrons. Consequently, the test standhas been modified for the current measurement campaign.
These modifications include the addition of new channels toacquire the high-voltage pulses from the modulator, as wellas signals necessary for calorimetry. These improvements
enable effective measurements of the klystrons performancein a reliable and secure testing environment.
For the klystron commissioning, an assembly consistingof a X-band high power load is connected to the klystron
output. At the end of the transmission line, an ion pumphas been integrated to maintain vacuum levels of approx.
10−8 mbar.
Two directional couplers (regular, DC, and high power,
HPDC) allow the measurement of the klystron’s input and
THPB: Thursday Poster Session
MC4.6 RF power sources and power couplers

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB016

P. Morales Sanchez*, N. Catalan Lasheras, A. Moros, A. Perez Fontenla, E. Rodriguez Castro,
S. Gonzalez Anton, A. Gerardin, A. Magazinik
CERN, Geneva, Switzerland
Abstract
This study presents the design and fabrication of a prototype normal-conducting X-band accelerator structure,
known as Smartcell. These structures, fabricated using
brazing and bonding techniques, are crucial for future linear colliders. We examine the brazing and bonding geometry, material selection, and the implications of varying
heat cycles and atmospheres during the brazing/bonding
processes. Additionally, we analyze how copper quality
and annealing procedures, conducted before, during, andafter machining, influence the machinability, microstructure, and overall performance of the final component. The
study evaluates different tests and five mock-ups, with results and conclusions drawn from optical examination, metrology, and scanning electron microscopy (SEM) analysis.

INTRODUCTION
Acceleration in the main linac of the Compact Linear
Collider (CLIC) [1] is based on normal-conducting, Xband travelling-wave structures working with a very highaccelerating gradient. Following extensive experiencefrom the NLC projects in the US and Japan, CLIC prototypes have been manufactured using ultra-precision (UP)machined copper disks, joined together through diffusion
bonding [2]. High-power tests on these structures havedemonstrated their capability to operate at a gradient of
100 MeV/m with a very low breakdown rate (BDR), meeting the stringent requirements set by CLIC [3].
However, advancements in machining accuracy, improvements in surface finishing, and new assembly methods, have significantly transformed the technological landscape. Within the CLIC collaboration, it has been shownthat brazed prototypes can achieve similar high-gradientperformance with low BDR [4], offering a viable alternative to diffusion bonding [5].
Considering these advancements, we have redesigned
the next prototype for CLIC, known as Smartcell, to be assembled by brazing, motivated by the advantages of using
lower temperatures and the broader availability of suppliers, which should lead to a cheaper production.
The following sections will discuss the design considerations, material selection, and fabrication processes involved in the Smartcell prototype, with a focus on optimizing the brazing process to ensure high performance and reliability and trying to keep the cost as low as possible.

CHOICE OF BRAZING PARAMETERS
In the initial phase of this redesigning process, available
UP machined cells (Fig 1) were repurposed for testing different parameters of the brazing cycle, namely Brazing
THPB: Thursday Poster Session
MC4.7 Room temperature RF

Filler Materials (BFM), brazing atmosphere, filling factor,
and applied pressure (Table 1). According to the BFM
specifications, the brazing cycles were conducted at temperatures between 790°C and 1010°C, with pressures from
4kPa to 40kPa (1-10 kg).

Figure 1: Existing disc model from an X-band accelerating
structure 11WNSDVG1.8.
Table 1: Test Cycles Parameters
#

BFM

1
2
3
4
5
6
7
8
9
10
11
12
13
14

AuCu50
AuCu50
AuCu50Palcusil5
Palcusil5
Palcusil5
Palcusil5
AuCu50
AuCu50
AuCu50Pallabraze840
Pallabraze840
Pallabraze840
Palcusil5

AtmosphereH2 dryH2 dryH2 dryVacuumVacuumVacuumVacuum
H2 dryH2 dryH2 dryVacuumVacuumVacuumVacuumFilling ratio
4.36
2.13
2.13
4.36
2.13
2.13
2.00
4.36
2.13
2.00
4.36
2.13
2.00
4.36

0.96
0.96
0.812
0.96
0.96
0.812
1.9
0.96
0.96
1.9
0.96
0.96
1.9
0.96

Weight
10
1
1
1
10
1
10
10
1
1
1
1
10
10

All specimens were vacuum tight, up to 1·10-10 bars. Ultrasound inspection showed good interface continuity.
Subsequently, we proceeded to cutting the samples andperformed optical microscope examination. Samples
brazed using AuCu50 at the highest temperature presented
crossing grains across the cell’s interfaces, demonstrating
successful diffusion bonding. In general brazing done with
Ag-based BFM did not present crossing grains and in mostcases, BFM flowed into the RF area. We performed an additional cycle #14, for which the heating cycle was extended by a long plateau (5 hours) right below the melting
temperature of the BFM to enhance diffusion bonding. As
anticipated, even at this relatively low pressure and temperature range 40kPa and 795.9°C, crossing grains were
present which indicated that diffusion bonding took place
THPB016659

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SMARTCELL X-BAND NORMAL CONDUCTING ACCELERATORSTRUCTURE PROTOTYPE FABRICATION

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB017

P. Korysko1∗ , I. Najmudin, C. Robertson, University of Oxford, Oxford, United Kingdom
R. Corsini, W. Farabolini, A. Aksoy, A. Malyzhenkov, A. Gilardi,
E. Granados, M. Martinez-Calderon, V. Rieker, L. Wroe, CERN, Geneva, Switzerland
1also at CERN, Geneva, Switzerland
Abstract
The CERN Linear Accelerator for Research (CLEAR)
at CERN is a user facility providing a 200 MeV electron
beam for accelerator R&D and irradiation studies, including
medical applications. In this paper we will outline the mostrecent improvements in CLEAR operation and beam control
and delivery, and describe the upgrades under way, giving an
update of their current status. These upgrades include a newfront-end for the laser system which will enable an highly
flexible time structure, better stability and higher repetition
rates, and the implementation of a second beam line which
will provide additional testing capability and whose optics
has been designed to match user requirements. Finally, we
will discuss the proposed future experimental program of
the facility, particularly in view of the novel capabilities
provided by the upgrades.

INTRODUCTION
The CLEAR facility offers a diverse array of electron
beams with customisable parameters [1–4], as detailed inTable 1. An overview of the time structure and charge parameters achievable at CLEAR, depicted in Fig. 1, alongwith a schematic layout of the beamline shown in Fig. 2.
Train length

Train spacing Train charge(10 pC – 87 nC)

ChargeCharge(0.1 ps - 100 ns)(0.1 – 1.2 s)(1 – 150 bunches) (0.833 – 10 Hz)

Bunch spacing(333 or 666 ps)

Bunch chargeTime(10 pC – 1.6 nC)

Bunch length(0.1 - 10 ps)

Time

Figure 1: CLEAR beam time structure and charge parameters at
the end of the beam line in 2024.
∗ pierre.korysko@cern.ch

THPB: Thursday Poster Session
MC2.2 Electron linac projects

Table 1: CLEAR Beam Parameters in 2024
Parameter
Beam Energy
Beam Energy Spread
Bunch length RMS
Bunch frequency
Bunch charge
Norm. emittanceBunches per pulse
Max. pulse charge
Repetition rate

Value
30 − 220 MeV< 0.2% rms (< 1 MeV FWHM)
0.1 − 10 ps
1.5 or 3.0 GHz
0.005 − 1.6 nC
1 − 20 µm
1 − 15087 nC
0.8333 − 10 Hz

CLEAR operates independently from CERN’s proton machines, enabling operation during the LHC’s extended shutdowns and upgrades. Offering remarkable flexibility, theaccelerator typically undergoes weekly experiment installations on Monday mornings and runs for 8 to 12 hours perday, five days a week, tailored to user demands. In 2023,
CLEAR ran for 37 weeks and the beam availability was
96.7% (40 hours of fatal failure for 1209 hours of beam).
In 2024, 35 experiments are planned in 39 weeks of beam.
The approval of the CERN Medium Term Plan in September
2020 earmarked funding for extended CLEAR operation,subsequently endorsed by CERN management until the endof 2025.
CLEAR provides two distinct in-air test areas: VESPER(Very energetic Electron facility for Space Planetary Exploration missions in harsh Radiative environments), primarily utilised for electronics radiation hardness tests, andthe In-Air Test Area offering greater flexibility for various
experimental needs. Both areas have been utilised for medical applications studies such as Very High Energy Electron(VHEE) radiotherapy at Ultra High Dose Rate (UHDR),
looking for the FLASH effect [5], beam instrumentation,
diagnostics studies and electronics component irradiation,
among others.
Notably, VESPER has played a role in testing and validating components for the ESA’s JUpiter ICy moons Explorer(JUICE) mission, successfully launched in April 2023 [6–9].
It is expected to reach Jupiter in July 2031 after four gravity
assists and eight years of travel. Additionally, CLEAR features in-vacuum test areas tailored for specific experiments,
including studies on novel accelerator technologies suchas plasma lenses and advancements in beam instrumentation [10, 11].
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OPERATIONAL IMPROVEMENTS AND UPGRADES
OF THE CLEAR USER FACILITY

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISSN: 2226-0366

doi: 10.18429/JACoW-LINAC2024-THPB018

MEDICAL ACTIVITIES IN CLEAR: STUDIES TOWARDSRADIOTHERAPY USING VERY HIGH ENERGY ELECTRONS (VHEE)IN THE FLASH REGIME
R. Corsini∗ , A. Aksoy, W. Farabolini, A. Gilardi, A. Malyzhenkov, CERN, Geneva, Switzerland
J. Bateman, M. Dosanjh 1 , P. Korysko 1 , C. Robertson
University of Oxford, Oxford, United Kingdom
V. Rieker1 , University of Oslo, Oslo, Norway
1
also at CERN, Geneva, Switzerland
Abstract
Given the present availability of high-gradient accelerator
technology for compact and cost-effective electron linacs inthe 100-200 MeV energy range, the interest for Very HighEnergy Electron (VHEE) radiotherapy (RT) for cancer treatment recently reached an all-time high. Particular significance is assumed by the Ultra-High Dose Rate (UHDR)
regime where the so-called FLASH biological effect takes
place, in which cancer cells are damaged while healthy tissue is largely spared. VHEE beams from linacs are especially well adapted for FLASH RT, given their penetration
depth and the high beam current needed to treat large deepseated tumours. In recent years, several multidisciplinary
user groups carried out a number of studies on VHEE andFLASH RT issues using the CERN Linear Accelerator for
Research (CLEAR) user facility, in close collaboration withthe local operation team. In this paper, we give an overview
of such activities and describe the main results of chemicaland biological tests aimed at clarifying the damage mechanisms at the root of the FLASH effect and the relevantbeam parameters needed to achieve it. We also describe
the dedicated systems and methods developed and used in
CLEAR for these activities, focusing on recent advances in
the crucial aspects of uniform beam delivery and high dose
rate real-time dosimetry.

INTRODUCTION
The CERN Linear Electron Accelerator for Research(CLEAR) is a 200 MeV electron linac followed by an experimental beam line, operated at CERN as a user facility [1].
It serves a wide and diverse scientific community covering many activities, including development of instruments
and components for existing and future accelerators andtests of novel concepts as plasma and THz acceleration. In
recent years, the investigation of medical applications ofelectron beams with energies above 100 MeV has become
one of its main activities. Over the past years, the questionof whether ultra-high-dose rate (UHDR) beams might offer
a new modality for cancer treatment is one of the most discussed subjects in modern radiotherapy (RT). The so-called
FLASH RT mode, in which the total therapeutic dose is delivered at UHDR in a fraction of a second, has been shown∗ roberto.corsini@cern.ch

THPB: Thursday Poster Session
MC3.1 Industrial and medical accelerators

in several experiments to significantly increase the differential response between healthy and tumour tissue [2–4].
Very-high-energy electron (VHEE) beams with energies
above 100 MeV are promising candidates for FLASH RT
due to their favorable dose distributions and accessibility ofultrahigh dose rates. Linear electron accelerators can easily
provide the high intensity beams needed for UHDR, and havethe additional advantage, thanks to recent advances in highgradient technology, of being rather compact and relatively
cheap. The CLEAR electron beam has a wide parameter
range, offering great flexibility for experiments [5–8]. In particular, CLEAR beam energy range (30-220 MeV) and highcharge per pulse (up to 75 nC) have made it so far the only
facility widely available to users for complete VHEE/UHDR
studies. Beam parameters are shown in Table 1. A diagramof the beamline is shown in Fig. 1.
Table 1: Updated List of CLEAR Beam Parameters
Parameter
Beam Energy
Beam Energy Spread
Bunch length rms
Bunch frequency
Bunch charge
Norm. emittanceBunches per pulse
Max. pulse charge
Repetition rate

Value
30 − 220 MeV< 0.2% rms (< 1 MeV FWHM)
0.1 − 10 ps
1.5 or 3.0 GHz
0.005 − 3 nC
1 − 20 𝜇m
1 − 15075 nC
0.8333 − 10 Hz

METHODS, DOSIMETRY AND BEAM
DELIVERY TECHNIQUESThe CLEAR team has developed in the last years methods
and data analysis techniques dedicated to VHEE and FLASH
studies, including detailed procedures for passive dosimetry
techniques, sample handling, and beam delivery. It also
explored new methods for real-time dosimetry in UHDR
conditions.
Radiochromic films (RCFs) change colour macroscopically due to polymerisation caused by ionising radiation.
The colour change is related to the accumulated dose. After
irradiation, the films are optically scanned and the resulting
image is processed to determine the dose received, using
an experimentally measured calibration curve. They are
THPB018
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ISBN: 978-3-95450-219-6

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ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB021

N. Solyak†, C. Edwards, I. V. Gonin, A. Saini, J. C. T. Thangaraj ,V. P. Yakovlev
Fermilab National Laboratory, Batavia, IL, USA
R. Kostin, Euclid Techlabs LLC, Bolingbrook, IL. USA
Abstract
Compact conductively cooled SRF industrial linacs canprovide unique parameters of the electron beam for industrial applications (up to 10MeV, 1MW). For ERDC project
we designed normal conducting RF injector with thermal
RF gridded gun integrated in the first cell. For design of
the RF gun, we used MICHELLE software to simulate andoptimize parameters of the beam. Output file was converted to ASTRA format and most beam dynamic simulations in multi-cell normal conducting injector and cryomodule were performed by using ASTRA software. For
cross-checking we compare results of MICHELLE and
ASTRA in first few cells. At the end of the injector the
beam reach ~250 keV energy which allow to trap bunch inacceleration regime without losses in TESLA like 1.3 GHz
cavity. Short solenoid at the end of injector allow to regulate transverse beam size in cryomodule to match beam to
extraction system and reduce charge losses in the injector.

INTRODUCTION
The new concept of a compact linear accelerator for industrial application suggested in Ref. [1] is based on use of
SRF cavities. Several proposals of the compact conduction
cooled linac received funding for the R&D stage. Attractive electron beam parameters for industrial application is
10 MeV with average beam powers of 100’s kW.
The Illinois Accelerator Research Center (IARC) of Fermilab has started design, construction, and validation of acompact 20 kW prototype of the linac capable of operating
10MeV, 2mA beam in a continuous wave (CW) mode
(ERDC project). The linac employs a 9-cells 1.3 GHz
TESLA-type Nb3Sn coated conduction-cooled cavity. As asource of electron beam, we propose to use external injector capable to produce bunches extracted from gridded RF
gun and accelerated in copper cavities up to 250-300 keV.
The general design of the gun is reported in [2, 3]. The engineering design of the cathode-grid unit has been done at
HeatWave Labs, Inc. and two prototypes were fabricated.
General layout of the linac, including RF injector cavity
with six individually controlled cells and cryostat with SC
9-cell cavity are presented in Figure 1. On the left side, one
can see resonator integrated with RF gun and providing RF
voltage on the grid. Playing with RF amplitude and DC
voltage on the grid and phase/amplitude of acceleratingcell allows us to get required 2 mA beam current and regulate bunch length, output energy and energy spread.

___________________________________________

Figure 1: General layout of the 20kW accelerator with external injector and superconducting 9-cells 1.3 GHz cavity.

RF GUN OPTIMIZATIONMICHELLE Simulation
The MICHELLE code [4] is a 3D electrostatic particlein-cell (PIC) code that has been designed to address thebeam optics modelling and simulation of charged-particle
transport. The MICHELLE approach uses space charge
limited emission based on the Child-Langmuir law.
The beam dynamics simulation of the RF gun + injector
cavity assembly was performed with MICHELLE code.
An RF voltage with a DC bias is applied to the cathodegrid gap to form the electron bunches. After emission,these bunches are captured and accelerated by RF field in
the gun-cell (C0) of the injector. The phase shift φ between
the RF fields in the gun and in the first cell is one of the
optimization parameters. Other parameters are DC and RF
voltages between cathode and grid.

Figure 2: Example of MICHELLE simulation of RF gun.
a) beam dynamics in the gun and accelerating cell. b) typical mesh-size: 25 μm-on the grid area, 200 μm in accelerating cell beam transportation area.
Figure 2 show geometry of the gun and cell and accelerated beam. For mesh size we chose fine mesh in cathodegrid area and near the axis of accelerating cell. Grid parameters were optimized for current of 2 mA and output energyof 30 keV after the first injector cell C0.

† solyak@fnal.gov.
THPB: Thursday Poster Session
MC1.2 Electron and ion sources, guns, photo injectors, charge breeders

THPB021671

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BEAM DYNAMICS SIMULATIONS FOR THE ERDC PROJECT:
INDUSTRIAL SRF LINAC

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB024

CW COPPER INJECTOR FOR SRF INDUSTRIAL CRYOMODULES
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R. Kostin†, C. Jing, Euclid Techlabs LLC
I. Gonin, V. Yakovlev, N. Solyak, T. Khabiboulline, C.Edwards, J. Thangaraj, FNAL, Batavia, USA
Abstract
Compact SRF industrial linacs can provide unique parameters of the beam (>1 MW CW and >1-10 MeV) hardly
achievable by normal conducting linacs within limited
space. SRF technology was prohibitively expensive until
the development of conduction cooling which opened theway for compact standalone SRF systems suitable for industrial and research applications. Limited cooling capacity puts strict requirements on the beam parameters withzero losses of the beam on the SRF cavity walls. This implies strict requirements on the beam energy to be acceptedby the cryomodule and most importantly the beam bunching with zero particles in between.
We designed a CW normal conducting RF injector which
consists of a gridded RF gun integrated with a first cell ofa copper booster cavity to satisfy these requirements. Here
we present a complete design of a booster cavity including
beam dynamics, RF, thermomechanical and engineering
design.

INTRODUCTION
The new concept of a compact linear accelerator for industrial application suggested in [1] is based on the use ofSuperconducting Radio-Frequency (SRF) cavities. Several
proposals of the compact conduction cooled linac has been
under development [2, 3]. Attractive electron beam parameters for industrial application is 10 MeV with average
beam powers of 100’s kW.
The Illinois Accelerator Research Center (IARC) of Fermilab has started design, construction, and validation of acompact 20 kW prototype of the linac capable of operating
10MeV, 2mA beam in a continuous wave (CW) mode
(ERDC project). The linac employs a 9-cells 1.3 GHz
TESLA-type Nb3Sn coated conduction-cooled cavity. As asource of electron beam, we propose to use external injector capable to produce bunches extracted from gridded RF
gun and accelerated in normal conducting CW injector up
to 250-300 keV. The general design of the gridded RF gun
is reported in [4, 5]. The engineering design of the cathodegrid unit has been done at HeatWave Labs, Inc. and two
prototypes were fabricated. This paper focuses on the injector preliminary design covering the whole spectrum ofengineering problems towards its fabrication.

1.3 GHz INJECTOR DESIGN
The schematic representation of the normal conducting
CW injector is presented in Fig. 1. The injector consists ofseveral accelerating single-cells boosting the beam energy
out of the grided gun up to 250-300 keV which is enoughto successfully capture the beam by the SRF Tesla-cavity

in the cryomodule which has all cells with β=1. The gridded RF gun is integrated into the first cell of the injector
cavity. Bunch length, output energy and energy spread canbe changed adjusting RF amplitude and DC bias of the gridand phase/amplitude of the first injector cell.

Figure 1: General layout of the normal conducting injector.
All of the cells of the injector are fed through their own
separate solid-state amplifiers (SSA’s) providing a lot offlexibility in cell’s design and beam manipulations. Single
cells can have higher shunt impedance as inter-cell coupling is not required and any phase advance can be realized
which gives improvement in transit time factor. RF focusing can also be employed. The injector will be locked to
the SRF cavity frequency. SRF Nb3Sn cavity is brittle, andthe mechanical tuning is not foreseen for the cavity, thus
the injector needs to have the ability of frequency adjustment of several 100’s kHz. RF tuning plungers are desiredin each cell for this purpose. A preliminary mechanical design of the injector is presented in Fig. 2.

Figure 2: Injector preliminary mechanical design.
The injector has total of six cells with different length toprovide the highest energy gain, not to match beam β as it
is not required due to each cell individual control. Each cell
has a pick-up probe, a loop-style fundamental power coupler (FPC), an RF plunger/tuner and vacuum port. Fourcooling channels at the cell’s OD are reserved for cavity
cooling. The next sections will focus on RF parameters,cooling, multipacting and beam dynamics.

___________________________________________† r.kostin@euclidtechlabs.com
THPB024674

THPB: Thursday Poster Session
MC2.2 Electron linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB026

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TRANSFER OF EP AND DOPING TECHNOLOGY FOR
PIP-II HB650 CAVITIES FROM FERMILAB TO INDUSTRY*
V. Chouhan†, D. Bice, S. Chandrasekaran, G. Eremeev, A. Netepenko, D. Passarelli, H. Park,J. Ozelis, G. Wu, Fermi National Accelerator Laboratory, Batavia, USA
A. Shabalina, Science and Technology Facilities Council, UK Research and Innovation, UK
P. Barbero1,2, A. Gresele1, A. Tsymbaliuk1,
1
Zanon Research and Innovation Srl, Italy,
2
Simic Spa, Italy
Abstract
Fermilab has optimized the surface processing conditions for PIP-II high beta 650 MHz cavities. This encompasses conditions for bulk electropolishing, heat treatment,
nitrogen doping, post-doping final electropolishing, andpost-processing surface rinsing. The technology has beeneffectively transitioned to industry. This paper highlights
the efforts made to fine-tune the process and to smoothly
share them with the partner labs and an associated vendor.

INTRODUCTION
The Proton Improvement Plan II (PIP-II) is an upgrade
to the Fermilab accelerator complex, designed to deliver an
800 MeV proton beam to create the world's most intense
neutrino beam for the Deep Underground Neutrino Experiment (DUNE). The PIP-II linear accelerator (LINAC) will
be developed with support from international partners andindustry, focusing on the integration of various types of niobium (Nb) superconducting RF (SRF) cavities into the
LINAC. The international partner laboratories responsiblefor delivering the high-beta (0.92) 650 MHz (HB650) cavities are Raja Ramanna Centre for Advanced Technology(India) and Science and Technology Facilities Council, UK
Research and Innovation (UKRI, UK), with additional support from industry. For UKRI, Zanon Research and Innovation Srl (Italy) is tasked with fabricating these cavities
and conducting the necessary surface processing.
Previous projects like LCLS-II and LCLS-II HE, led by
the United States with industrial collaboration, have set a
successful precedent. The achievements of these projects
were made possible through effective technology sharing
with industry partners [1, 2]. Surface processing of the Nbcavities is a critical step in ensuring the cavities meet theperformance specifications required for the cryomodules.
The knowledge gained from these projects is invaluable for
future endeavors and is currently being applied to the ongoing PIP-II project.
This paper reports on the surface processing technology
and the lessons learned, which have been shared with partner labs and the vendor working on the HB650 cavities.

___________________________________________* This work was supported by the United States Department of Energy,
Offices of High Energy Physics and Basic Energy Sciences under contract No. DE-AC02-07CH11359 with Fermi Research Alliance.
† vchouhan@fnal.gov

THPB026
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LESSONS LEARNED ON EP OF HB650
Fermilab and other SRF facilities have extensive
experience in electropolishing (EP) 1.3 GHz cavities andother surface processing techniques [1, 3]. The HB650
cavity is significantly larger, with nearly twice the surface
area of a 1.3 GHz cavity, making the same standard EP
conditions unsuitable for achieving a smooth surface, as
shown in our latest EP study conducted with LB650 and
HB650 cavities [3, 4]. Based on the studies performed, key
findings and lessons learned were identified assummarized below.
The standard 18 V was found to be insufficient for the
EP of HB650 cavities, resulting in a rough equator surface
and premature quench of the cavities [3]. This conclusion
is supported by I-V curves measured for 650 MHz cavities
under various conditions. The I-V curve with two major
regions, linear and plateau regions, provides insight into
the chemistry of the cavity surface. A smooth surface isachieved when EP is conducted at a voltage within theplateau region.

Figure 1: I-V curves measured for 1.3 GHz and HB
650 MHz cavities. The I-V curve for HB650 was obtainedwith new cathode structure.
Unoptimized cathode structure and surface area fail toyield the current plateau even up to 25 V [3]. A new cathode was designed to enhance the surface area and acid flow
conductance, and to reduce cathode polarization. The plateau onset (Vonset) was obtained at relatively lower voltage
as compared to the initial cathodes. A lower EP voltage isalso important to mitigate sulfur generation. However,
HB650 cavities still requires an EP voltage higher than thestandard voltage. The I-V curves for a 1.3 GHz 9-cellcavity and an HB650 cavity are compared in Fig. 1. Vonset

THPB: Thursday Poster Session
MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB027

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STUDY OF MECHANICAL GRINDING EFFECTS
ON NIOBIUM SURFACE*
V. Chouhan†, T. Ring, D. Smith, G. Wu, Fermi National Accelerator Laboratory, Batavia, IL, USA
Abstract
Mechanical grinding is commonly employed to eliminate surface defects such as scratches and pits from niobium cavity surfaces or sheets before cavity fabrication.
Subsequently, chemically buffered polishing or electropolishing is often utilized to completely remove residues of the polishing media and any defects induced bymechanical grinding, ensuring a pristine surface. In thisstudy, we conducted a systematic investigation to assess
the influence of mechanical grinding using silicon carbide
and aluminum oxide polishing media on niobium surfaces.
Additionally, the study examines the effects of post-mechanical grinding chemical treatments on surface quality.

INTRODUCTION
Niobium (Nb) superconducting RF (SRF) cavities formodern superconducting accelerator machines are fabricated by following various steps, including Nb sheet fabrication from Nb ingot deep drawing, electron beam welding, buffered chemical polishing (BCP), electropolishing(EP), and other surface processing methods [1, 2]. Mechanical grinding is also required at different stages to polishthe surface defects when they appear. Surface grinding isoften applied during the preparation of the Nb sheet, before
deep drawing the sheets to form half cells, and even to afabricated cavity when a defect appears on the interior surface.
The thickness of the cavity wall must be maintained at adesired value, and the surface should be defect-free as required for the good performance of the cavities. Therefore,a precise grinding process is essential [3], typically using
silicon carbide (SiC) or aluminum oxide (Al2O3) media.
However, understanding the optimal grinding media, gritsize, and post-grinding removal through BCP or EP for Nb
remains limited.
This study aims to provide insights into the grinding process and the necessary EP removal to achieve a defect-freesurface, free from embedded contaminants.

EXPERIMENTAL
Nb samples (1×1 cm) were prepared from the same Nb
sheet. The samples were electropolished for 100 µm removal to eliminate any initial surface defects. These electropolished samples were mechanically ground using SiC
and Al2O3 media with varying grit sizes. A target sample
was pressed against a rotating disk with sandpaper attached
for grinding. For each media type, 5 samples were groundinitially with grit size 80 and finished with finer grits___________________________________________* This work was supported by the United States Department of Energy,
Offices of High Energy Physics and Basic Energy Sciences under contract No. DE-AC02-07CH11359 with Fermi Research Alliance.
† vchouhan@fnal.gov

THPB027682

ranging from 120 to 320. The grinding steps and average
removal are detailed in Table 1.
After grinding, all samples underwent three EP sequences, removing a total of 20, 40, and 80 µm. EP was
performed in a temperature-controlled electrolyte bath using a standard mixture of sulfuric (96wt%) and hydrofluoric (70wt%) acids in a 10:1 volumetric ratio. EP was conducted at 18 V, with Nb as the anode and an aluminum electrode as the cathode.
The sample surfaces were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to identify any embedded particles. Laser
confocal scanning microscopy (LCSM) was used to study
surface morphologies to assess the effects of grit size andremoval on the surface quality.

RESULTS AND DISCUSSION
After grinding, all the surfaces were observed using
SEM and analyzed with EDS. Figure 1 shows typical SEM
images of the niobium surfaces ground with grit sizes 80
and 320 of SiC and Al2O3. The coarse grit of 80 clearlycaused more surface damage, as observed for both SiC andAl2O3 media. It was evident that grinding with SiC, especially with grit size 80, resulted in greater surface damage
compared to Al2O3. Additionally, the SEM images revealed
bright spots, which are presumed to be embedded abrasive
particles. The number of bright spots increased with finer
grit sizes for both types of media. However, the surfaces
ground with SiC consistently exhibited more bright spots
compared to those ground with Al2O3.
To analyze these bright spots, EDS was performed on all
the samples. Figure 2 presents the EDS spectra of the surfaces of SC-G320 and AO-G320, which were ground witha fine grit size of 320 and contained the highest number ofbright spots. The EDS spectra for SC-G320 and AO-G320
show peaks corresponding to Si and Al, indicating the presence of embedded SiC and Al2O3 abrasives in the niobium
surface. The strong Si peak confirmed that the surfaces
ground with SiC contained a higher number of embedded
particles compared to those ground with Al2O3.
After the EP steps, the samples were again examined using SEM and EDS to detect any remaining embedded particles. Thorough SEM scanning and EDS analysis revealed
that no embedded SiC particles remained after the first EP
step, which removed 20 µm of material. However, some
Al2O3abrasives were still embedded in the surfaces of samples AO-G80 and AO-G320. Figure 3 shows an SEM image of AO-320 after the first EP step, along with its corresponding EDS spectrum. The image and spectrum indicate
the presence of an embedded Al2O3particle. However, after
subsequent EP steps, no abrasives were detected on any of
the samples.
THPB: Thursday Poster Session
MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB028

V. Chouhan†, D. Bice, A. Cravatta, T. Khabiboulline, O. Melnychuk. A. Netepenko, G. Wu
Fermi National Accelerator Laboratory, Batavia, IL, USA
B. Guilfoyle, T. Reid, Argonne National Laboratory, Lemont, IL, USA
Abstract
Electropolishing process and cathodes have undergone
modification and optimization for both low- and high-beta
650 MHz five-cell niobium cavities for PIP-II. Cavities
treated with these modified electropolishing conditions exhibited smooth surfaces and good performance in baseline
tests. Nonetheless, due to administrative constraints on
project cavities, maximum gradient performance testing
was not conducted. This paper presents a study conducted
on a single-cell 650 MHz cavity utilizing the optimized
electropolishing conditions, highlighting the maximum
performance attained for this specific cavity. The cavity
tested at 2 K in a vertical cryostat reached a superior accelerating field gradient of 53.3 MV/m at Q0 of 1.61010,
which is the highest gradient attained for this type of largesized cavities.

INTRODUCTION
Modern superconducting accelerator machines utilize
niobium superconducting RF cavities, which operate in asuperconducting state at 2 K. Various types of superconducting cavities are essential for building an efficient accelerating machine. Medium (~650 MHz) and high frequency (~1.3 GHz) elliptical cavities are used to accelerate
high-energy particles. For an efficient accelerator, it is crucial to have cavities with both high gradient and high Q₀.
SRF R&D focuses on enhancing these aspects, with surface processing playing a critical role in achieving optimal
performance. Key processes include electropolishing, heat
treatment, nitrogen doping (N-doping), mid-temperature
baking, 120°C baking, and high-pressure water rinsing.
Electropolishing is an electrochemical technique designed
to remove interior material from the cavity, ensuring a defect-free and smooth surface.
1.3 GHz cavities have demonstrated excellent SRF performance with a high accelerating gradient of around 50
MV/m [1]. The corresponding surface peak magnetic field
Bpk reaches ~210 mT. 650 MHz niobium cavities should
also be capable of reaching similarly high gradients andcorresponding Bpk. However, the performance of 650 MHz
cavities and cavities with similar frequencies reported so
far have not met such a high performance.
Recently, we have demonstrated significant improvements in the surface quality and SRF performance of lowand high-beta five-cell 650 MHz cavities developed for theProton Improvement Plan (PIP-II) linac [2, 3]. Notably,___________________________________________

one of the HB650 cavities was tested beyond the administrative limit, achieving 29 MV/m without quenching [3].
The maximum performance potential of these cavities, following processing with the modified EP technique and upgraded cathode design, has yet to be fully assessed. This
study focuses on applying the optimized EP conditions toa 650 MHz single-cell cavity with a  value of 0.9 and evaluating its maximum quench field. This paper presents thesurface processing methods applied and the resulting SRF
performance of the 650 MHz single-cell cavity.

EP SETUP AND CONDITIONSThe horizontal electropolishing (EP) setup and the cathode used in this study are illustrated in Fig. 1. The singlecell cavity (B9AS-AES-003) was processed using EP parameters detailed in Table 1. The cathode design used forthe 5-cell cavities was scaled down and replicated for thecavity B9AS-AES-003. These EP parameters and cathodestructure were consistent with those optimized for the 5cell high- 650 PIP-II cavities [3].

Figure 1: EP tool with the cavity B9AS-AES-003 (top). Patented cathode structure used for EP the cavity (bottom).

* This work was supported by the United States Department of Energy,
Offices of High Energy Physics and Basic Energy Sciences under contract No. DE-AC02-07CH11359 with Fermi Research Alliance.
† vchouhan@fnal.gov
THPB: Thursday Poster Session
MC4.8 Superconducting RF

THPB028
685

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EXCELLENT PERFORMANCE OF 650 MHz SINGLE-CELL
NIOBIUM CAVITY AFTER ELECTROPOLISHING*

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OPTIMIZATION OF STATIC HEAT LOADS OF THE PIP-II CRYOMODULES
BASED ON PROTOTYPE HB650 CRYOMODULE TEST RESULTS*
V. Roger †, J. Bernardini, B. J. Hansen, J. P. Holzbauer, J. Makara, A. Martinez, J. Ozelis,
D. Passarelli, M. J. White, D. Porwisiak, S. Yoon, J. Subedi, Fermilab, Batavia, USA
Abstract
During the first cool-down of the prototype HB650 cryomodule (pHB650 CM), high static heat loads have beenmeasured compared to the estimation. Several analysis andcalculations have been performed to explain this difference
which led to cool-down this cryomodule two additionaltimes. Before each cool-down, repairs and upgrades havebeen done, and instrumentations were added to identify theissues and quantify their impact on the heat loads. Basedon these findings, the production cryomodule design andassembly process have been updated to align the future
heat loads measurements with the estimations.

INTRODUCTION
From March 2023 to July 2024, the pHB650 CM underwent three cooling cycles. Extensive cryogenic testing conducted during the initial cooldown, detailed in Table 1,
prompted a thorough analysis to identify discrepancies between calculated and measured static isothermal heat loads[1]. The analysis revealed several issues:• Radiation from the room temperature parts of the couplers inside the coldmass.
• Thermal Acoustic Oscillations (TAO) in the cooldown valve.
• Rollin film going up in the pressure transducer lines
making a short with the thermal shield.
In addition, heat loads estimations were checked and refined using a Simulink/Simscape model of the pHB650
CM [2] supplemented by measurements obtained from the
1st cool-down.
Table 1: Estimated and Measured Static Heat Loads

High Temperature Thermal Shield (HTTS)
Low Temperature Thermal Source (LTTS)
2K (Cavities at 4K)
2K (Cavities at 2K)

Estimatedheat loads

1st Cooldown

160 W

260 W

17.6 W

29.7 W

9.8 W
10.1 W

33.8 W~ 50 W

STATIC HEAT LOADS MEASUREDDURING THE 1ST AND 2ND COOL-DOWN
Prior to the 2nd cool-down of the cryomodule, several
modifications were implemented, Multi-Layer Insulation(MLI) was added around the room temperature parts of the___________________________________________* This manuscript has been authored by Fermi Research Alliance, LLC
under Contract No. DE-AC02-07CH11359 with the U.S. Department ofEnergy, Office of Science, Office of High Energy Physics.
† vroger@fnal.gov
THPB029688

couplers, the material of the cool-down valve stem has
been changed from Stainless steel to G10, and heaters havebeen added at the base of the pressure transducer lines. Following overseas transportation, which aimed to validate
the design of the cryomodule and its transport frame [3], a
3rd cool-down was conducted. During this phase, additional
MLI was applied around the couplers, a check valve wasinstalled on the relief line, and heaters along with temperature sensors were added to the valve intercepts. Additionally, a light warm-up procedure was performed to facilitate
the replacement of the G10 stem with a stainless-steel stem
equipped with wipers, similar to the method used for the
LCLS-II cryomodules [4]. Heat loads results for the 2nd and3rd cool-down are summarized in Table 2.
Table 2: Measured Static Isothermal Heat Loads During
Cool-Downs
HTTS
LTTS
2K
(Cavities
at 4K)

2nd Cool-down
240 W
23.3 W

3rd Cool-down
240 W
19.5 W

27.2 W

23.0 W

29.6 W
27.5 W(Before(After
38.2 W
putting
putting
wipers)wipers)An analysis of the heat loads for both the Low Temperature Test Stand (LTTS) and the 2K stage with cavities at
4K, indicates that radiation from the room temperatureparts of the couplers impacts both LTTS and 2K heat loads
similarly. To address the discrepancies observed between
the estimated and measured heat loads, the contributions of
the main components of the cryomodule [5] have beenstudied in detail in the subsequent chapters.
2K(Cavities
at 2K)

CRYOGENIC VALVES
During the 1st cool-down of the cryomodule, TAO wereobserved in the cool-down valve. Although replacing thestainless-steel stem with a G10 stem during the 2nd cooldown reduced the heat load associated with TAO by approximately 5.2 W, it did not completely eliminate the issue. TAO were fully mitigated in the final phase of the 3rdcool-down after installing wipers on the stainless-steel
stem, which reduced the heat load by an additional 2.1 W.
The installation of temperature sensors on the valve intercepts during the 3rd cool-down (as shown in Fig. 1) enabled the calculation of heat transfer through the thermal
straps with cavities at 2K and 8K for which TAO are notpossible. The comparison of this data confirmed that theTAO issue in the cool-down valve was effectively
THPB: Thursday Poster Session
MC4.2 Cryomodules and cryogenics

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THE 648 MHz KLYSTRON POWER SOURCE SYSTEM OF CSNS-II LINAC
SUPERCONDUCTING ELLIPSOID CAVITY
Zhencheng Mu1, Maliang Wan1, Hui Zhang2, Xie Zhexin1, Hexin Wang1, Bo Wang1, Linyan Rong1
1
Institute of High Energy Physics, Beijing, China
2
Spallation Neutron Source Science Center, Dongguan, China
Abstract
The CSNS-II superconducting Linac accelerator includes 20 sets of 324 MHz superconducting spoke cavities
and 24 sets of 648 MHz superconducting ellipsoidal cavities. The beam energy at the end of the superconducting
Linac accelerator reaches 300 MeV. The 324 MHz solidstate power source supplies RF power to superconducting
spoke cavity, while the 648 MHz klystron power source
supplies RF power to superconducting ellipsoid cavity. The
RF pulse width of the 648 MHz klystron is 1.2 ms, the repetition rate is 5 0Hz, and the peak power is 1.2 MW. The
1.5 ms long pulse solid-state modulator provides high voltage pulse for the klystron, and each modulator is equippedwith four klystrons.

INTRODUCTION
At the end of March 2024, the phase II of China Spallation Neutron Source (CSNS-II) project began, 20 sets of
324 MHz spoke cavities are connected behind the DTL accelerators, the spoke cavities increase the energy of the Hions from 80 MeV to 173 MeV. Then, 24 sets of 648 MHz
medium β ellipsoidal cavities further increase the energy of
the H- ions to 300 MeV.

THE RF POWER SOURCE SYSTEMSThe RF power source systems provide RF power required for 50 mA of peak beam current over a pulse lengthof 700 μs at a repetition rate of 50 Hz. The beam cutting
rate is 40%. The fill and fall time of the ellipsoidal cavities
will be on the order of 300μs, the RF pulse length of the
RF power source is set 1.2ms, the duty factor of the RF
power is 6%. The RF peak power demands of the CSNS
Linac superconducting cavities are shown in Fig. 1. According to the RF peak power demand, the 324 MHz spoke
cavities are powered by solid state amplifiers, and the648 MHz klystron power sources are adopted to supply RF
power for superconducting ellipsoidal cavities.

THE 648 MHz KLYSTRON POWER
SOURCE OF ELLIPSOID CAVITY
Each 648 MHz klystron power source of ellipsoidal cavities consists of a modulator, a 648 MHz klystron, a circulator and dummy load, WR1500 waveguides to deliver the
RF power to cavities. One modulator provides the highvoltage pulse to four klystrons.

Klystron
The klystrons operates at a frequency of 648 MHz andthe saturation peak power is 1.2 MW. With the 6% duty
cycle for CSNS-II Linac RF system, this means that the
average power level at saturation is about 72kW, the specifications of the 648 MHz klystron are shown in Table 1 [1].
Table 1: The Specifications of 648 MHz Klystron
Parameter

Value

Center Frequency
Bandwidth
RF Peak PowerRF Pulse Width
Repetition rate
Gain
Efficiency
Cathode Voltage

648
±0.5
≥1.2
1.2
50
≥45
50
-105

Unit
MHz
MHz
MW
ms
Hz
dB
%
kV

The 648 MHz klystron is designed with mod-anode configuration, and the modulator outputs high voltage pulse to
the klystron cathode, the high voltage pulse applied to the
mod-anode can be adjusted through resistive divider. The
electron gun part of the klystron includes two section ceramics, this part is placed in an oil tank to protect the ceramics from high voltage breakdown. After receiving theprototype of the 648 MHz klystron, we aged the klystronwith a hi-potter, and the withstand voltage between the
mod-anode and the cathode was aged to 90 kV, the withstand voltage between the mod-anode and the ground wasaged to 70 kV. The prototype passed the site acceptance testin October 2023, the test results have met all the specification requirements. The 648 MHz klystron operates in horizontal orientation, it has a separate magnet, and the photograph of the klystron installed at CSNS site is shown isFig. 2.

Figure 1: RF power demands of spoke cavities and ellipsoidal cavities.

THPB032692

THPB: Thursday Poster Session
MC4.6 RF power sources and power couplers

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB033

Z. Sun†, T. Xin, X. Li, C. Meng, O. Xiao, Z. Liu
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
also at University of Chinese Academy of Sciences, Beijing, China
Z. Song, Tsinghua University, Beijing, China
Abstract
For experiments requiring the longitudinal shaping of
the beam at the exit of an electron linear accelerators, it is
crucial to infer the initial beam profile at the entrance ofthe linear accelerator and key parameters. After passing
through the dispersion section of beam bunch compressor,
and the high-frequency system, the electron beam will undergo modulation on the longitudinal density. Based on thelongitudinal dynamic process, this paper proposes to use
automatic differentiation to provide the design of beam initial conditions and key parameters corresponding to a specific longitudinal profile of the beam at the exit of the linear
accelerator. Finally, we implemented this method on a section of linear accelerator consisting of two L-band accelerating cavities, one S-band accelerating cavity, and a bunch
compressor.

INTRODUCTION
The advancement of accelerator technologies, including
free-electron lasers, terahertz radiation sources, and plasma
accelerators, underscores the critical need for precise control over the temporal characteristics of electron beams [1].
These applications benefit from customized current profiles, which are vital for achieving optimal performance.
For example, in plasma acceleration, specialized electron
beam profiles play a key role in achieving high transformer
ratios. This often involves using an asymmetric driver
beam with a triangular shape, characterized by a gradualincrease in density at the front and a sharp decrease at therear to minimize the decelerating field experienced by thedriver beam. Furthermore, utilizing a trapezoidal distribution for the beam to be accelerated results in a flatter longitudinal wakefield at the accelerated beam's location, facilitating the production of a beam with low energy spreadfor efficient acceleration [2]. Additionally, the eliminationof current fluctuations is crucial for enhancing the operation of free-electron lasers, underscoring the significanceof advanced beam shaping techniques in accelerator physics for designing optimal current profiles for various FEL
applications. To address these requirements, shaping the
temporal profiles of electron beams is indispensable, emphasizing the importance of advanced beam shaping techniques in accelerator physics.
Several reliable methods have been developed to shapethe beam profiles. One common method involves directing
an electron beam with a particular energy spread throughan energy dispersion section, such as a bunch compressor
with multiple bending magnets, and possibly additional†sunzheng@ihep.ac.cn
THPB: Thursday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

sextupoles and octupoles [3]. These components offer amore flexible combination of dispersion terms. By selecting the appropriate combination of parameters in the compressor and an initial beam with a particular energy chirp,
it is possible to achieve the desired beam profiles. Furthermore, understanding the impact of the RF system on theenergy chirp, and anticipating the longitudinal distributionof the beam in advance, will be a crucial step. This is also
the main issue that this paper work aims to address.
With the application of automatic differentiation in thereconstruction of beam phase space, more and more attention is being focused on using automatic differentiation tosolve problems with high complexity, high dimensionality,and difficulties in convergence. R. Roussel and A. Edelen's
team proposed using automatic differentiation techniques
to rapidly reconstruct the 6-dimensional information of theinitial beam based on neural network structures, utilizing
the 6-dimensional information of the beam images observed at the diagnostic screen [4]. This laid the foundation
for the application of automatic differentiation techniquesin solving inverse problems.
Based on this method, we analyzed the longitudinal dynamics of the beam and provide the relationship between
the longitudinal particle coordinates of the beam at the exit
and the initial RF system parameters, chicane parameters,
and initial particle longitudinal coordinates. By using automatic differentiation methods, the initial beam profile andthe parameter design of the linear accelerator can be rapidly determined.

LONGITUDINAL DYNAMICS
For generality, we discuss the longitudinal dynamics
process of an electron beam passing through an RF system
consisting of two L-band traveling wave tubes and one Sband traveling wave tube, as well as a chicane design similar to that described in Ref. [3] (comprising 4 dipoles and2 quadrupoles, 2 sextupoles, and one octupole, providing amore flexible combination of dispersion terms) as shownin Fig 1. Assuming the initial electron beam is monoenergetic with an initial energy of 200 MeV, the electron energy(charge e) at the chicane after passing through the three RF
systems is
E f  E0  eV1kL cos(1  kL Z0 )  eV2 kL cos(2  kL Z0 )  eV3ks cos(3  kS Z0 )(1)
where kL , S  (2  L ,S ) is the RF wavenumber, z0 is thelongitudinal position of the electron with respect to thereference particle (bunch center), and the bunch head is at
THPB033
695

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INVERSE INFERENCE OF INITIAL BEAM PROFILE AND KEY PARAMETERS BASED ON AUTOMATIC DIFFERENTIATION METHOD*

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COMPLETION OF PHASE B+ BEAM COMMISSIONING OF
LINEAR IFMIF PROTOTYPE ACCELERATOR (LIPAc)*
T. Akagi†, 1, A. De Franco1, T. Ebisawa, K. Hasegawa, K. Hirosawa1, J. Hyun1, N. Kaneko1,
A. Kasugai, K. Kondo, K. Kumagai1, S. Kwon1, K. Masuda1, A. Mizuno4, M. Sugimoto1
QST, Rokkasho, Japan
2
1
F. Benedetti , Y. Carin , J. Chambrillon1, F. Cismondi, H. Dzitko, D. Gex1, D. Jimenez-Rey3,
I. Moya1, F. Scantamburlo1, F4E, Garching, Germany
1
also at IFMIF/EVEDA Project Team, Rokkasho, Japan2
also at CEA Paris-Saclay, France
3
also at CIEMAT, Madrid, Spain
4also at JASRI, Sayo, Japan
Abstract
The Linear IFMIF Prototype Accelerator (LIPAc) is being commissioned under the international collaboration between the EU and Japan. LIPAc aims to accelerate a deuteron beam of 125 mA to 9 MeV and operate in CW mode,and consists of an injector, an RFQ, a Superconducting RF
Linac (SRF Linac), a beam transport line, and a beam
dump. Until recently, the LIPAc beamline was in its final
configuration except for the SRF Linac, which was for ahigh-duty beam operation called Phase B+ commissioning.
The main objective of this commissioning was to validatehigh duty cycle deuteron beam operation and characterization of the beam. Phase B+ was completed at the end ofJune 2024, with a beam current of about 119 mA and duty
cycle of up to 8.75% have been achieved. After the completion of the Phase B+, the SRF will be delivered to theaccelerator room and installed in the beamline. The resultsof Phase B+ are presented in this paper.

INTRODUCTION
As one of the Broader Approach (BA) projects, an international cooperation between Europe and Japan in the fieldof fusion energy, the International Fusion Materials Irradiation Facility (IFMIF) Engineering Validation and Engineering Design Activity (IFMIF/EVEDA) is underway [1].
This is to research and develop an accelerator-driven intense neutron source using the D-Li stripping nuclear reaction to study the effects of 14 MeV high-energy neutrons
produced in the D-T fusion reaction on potential candidate
materials constituent of a fusion reactor.
The prototype accelerator of IFMIF, called Linear IFMIF
Prototype Accelerator (LIPAc), is being commissioned in
Rokkasho-mura, Japan as part of the IFMIF/EVEDA project. The IFMIF accelerator concept is designed to operate
in continuous wave (CW) mode with two deuteron beams
with a total of 250 mA (2 × 125 mA) at 40 MeV. LIPAc isdesigned to demonstrate the low-energy part of the accelerator, which is the most challenging part from a beam dynamic standpoint, and its goal is to accelerate a 125-mA
deuteron beam to 9 MeV and operate in CW mode. LIPAc___________________________________________* IFMIF/EVEDA Integrated Project Team with
QST, IFMIF/EVEDA PT, F4E, CEA, CIEMAT, INFN
† akagi.tomoya@qst.go.jp
THPB036698

consists of an injector, an RFQ driven by 175 MHz eight
200 kW RF power system, an SRF Linac, a beam transportsystem and a Beam Dump (BD). Each system was designed and manufactured at European research institutes
and shipped to QST Rokkasho Institute for Fusion Energy
in Rokkasho for installation and commissioning. The commissioning of LIPAc is performed in several phases: Injector Stand-Alone Validation (Phase A), RFQ Validation(Phase B) and SRF-Linac Validation (Phase C/D) as shownin Fig. 1. Phase B was completed in July 2019 with the successful acceleration of a 125-mA deuteron short pulse
beam (1 ms, 1 Hz) at 5 MeV thanks to the RFQ [2]. The
installation of the MEBT Extension Line (MEL) in placeof the SRF Linac, the High Energy Beam Transport(HEBT) line and the beam dump enabled to begin the
Phase B+ in 2021 toward high-duty beam operation and it
was completed at the end of June 2024. The SRF Linac installation preparations are currently underway for Phase C.
The following sections report on the test results obtained
from the Phase B+.

Figure 1: The three configurations of the LIPAc stepwise
commissioning phase.

PHASE B+The main purpose of Phase B+ is to demonstrate the operation of the 5 MeV deuteron beam with long pulses andto characterize the beams injected into the SRF-Linac(which will be installed after the completion of Phase B+).
THPB: Thursday Poster Session
MC3.2 Ion linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA

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PLAN FOR TERAHERTZ-WAVE SOURCE OF SUPERIMPOSEDCOHERENT TRANSITION RADIATIONUSING RING-TYPE RESONATOR AT LEBRA
N. Sei†, H. Ogawa, Research Institute for Measurement and Analytical Instrumentation,
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
T. Sakai, Y. Hayakawa, Y. Takahashi, T. Tanaka, K. Hayakawa
Laboratory for Electron Beam Research and Application, Nihon University, Funabashi, Japan
T. Takahashi, Institute for Integrated Radiation and Nuclear Science,
Kyoto University, Osaka, Japan
Abstract
We plan to generate high peak power pulses in a terahertz region by superimposing CTR pulses using a ringtype resonator. In experiments conducted at an L-band
electron linear accelerator facility at the Kyoto University
Institute for Integrated Radiation and Nuclear Science(KURNS-LINAC), a resonant coherent transition radiation(CTR) could be extracted with low loss from the resonatorusing a material with low absorption in the terahertz region
as an output coupler inside the resonator. It was observedthat the extracted terahertz CTR pulses were amplified owing to superimposition of their electric fields. Because thelong CTR wavelength resulted in large diffraction losses of
the resonator, the amplification rate of the CTR pulses was
low at the KURNS-LINAC. We therefore planned to develop a device of CTR superposition with a ring-type resonator at the Laboratory for Electron Beam Research andApplication (LEBRA) in Nihon University, where a shortwavelength CTR has been developed using the electron
beam with the bunch length of a few sub-picoseconds isshort. Our goal is to generate terahertz CTR pulses with apeak power of more than 1 MW at the LEBRA.

INTRODUCTION
We have studied intense terahertz-wave sources using anormal-conducting S-band linac at the Laboratory for Electron Beam Research and Application (LEBRA) at Nihon
University [1, 2]. The developed coherent transition radiation (CTR) had a high energy of 1 mJ per macropulse [3].
However, the peak power of the CTR was approximately
100 kW and did not reach 1 MW, i.e., the level at which
nonlinear optical phenomena are evident in the terahertz
region. Therefore, based on our experimental results at the
Kyoto University Institute for Integrated Radiation and
Nuclear Science (KURNS-LINAC) [4], we planned to generate high peak-power terahertz pulses by confining CTR
micropulses in a ring-type resonator and superimposing
them with CTR micropulses generated late within the resonator. By inserting a plate with low absorption in the terahertz region into the resonator as an output coupler, it ispossible to extract CTR pulses with high peak power while
suppressing a cavity loss.
In this article, we first briefly describe pulse superposition of coherent radiations using a resonator. Then, we outline the superposition experiments of CTR micropulses___________________________________________† sei.n@aist.go.jp

conducted at the KURNS-LINAC and describe the plan of
the new superposition experiments at the LEBRA.

PULSE SUPERPOSITION USINGA RESONATOR
Coherent radiation has an electric field structure whichcorresponds to a pulse shape of an electron bunch [5]. If abunch train in an electron beam macropulse is accelerated
at precise time intervals, the coherent radiation train generated by the electron bunches can be superimposed by confining them in a resonator whose circumference is an integer multiple of the electron bunch interval. The electricfield of the superimposed coherent radiation can be amplified by using a resonator comprising an even number ofmirrors. Several studies on the superimposition of coherent
radiations using a resonator have already been reported[6, 7].
If a CTR in the terahertz region generated by a thin metal
substrate is used as a coherent radiation source, the substrate can be also used as a mirror to construct the resonator[4]. To extract CTR pulses from the resonator, a thin parallel plate made of a material with negligible absorption in
the terahertz region is used. When the parallel plate is inserted at the Brewster angle with respect to the circulating
CTR pulses, the p-polarized component of the CTR pulses
passes through the parallel plate without a loss. Therefore,
it is possible to construct a resonator with a small cavity
loss. The CTR pulses are observed using the s-polarizedcomponent extracted from the resonator. By adjusting the
thickness of the parallel plate whose optical length islonger than the length of the CTR pulse, interreference ofreflected lights on the front and back surfaces of the parallel plate can be eliminated. If the CTR pulse length is sufficiently short, even materials with a slightly high absorption can be used as the parallel plate. When a semiconductor material is irradiated with a short-pulse laser, a plasma
mirror which reflects lights in the terahertz region is generated [8]. Using Si as the parallel plate, it is possible toquickly extract the high peak-power CTR pulses accumulated in the resonator.

SUPERPOSITION EXPERIMENTS
AT KURNS-LINAC
A ring-type resonator comprising two off-axis parabolic
mirrors and two plane mirrors was installed on the electron
beam orbit of an L-band electron linear accelerator facility

THPB037

THPB: Thursday Poster Session702

MC2.7 Synchrotron light sources

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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INTEGRATION OF HKL SINGLE CRYSTAL COMPUTATIONS INTO
EPICS USING PYDEVICE ∗Alexander Baekey1,2 , Kazimierz J. Gofron1†
1
Oak Ridge National Laboratory, Oak Ridge, TN, USA
2
University of Central Florida, Orlando, FL, USA
Abstract
In this work, we integrate and extend an HKL computation
package into EPICS through a PyDevice IOC. This provides
EPICS users a generalized approach to mapping real motor
rotation space to HKL reflections for a wide range of diffractometers (4-circle, 6-circle, kappa geometries). Utilizing
PyDevice for EPICS IOC development allows us integrate
Python bindings for core calculations written in C, simultaneously taking advantage of the efficiency of C and readabilityof Python. The EPICS IOC provides an interface between
beamline hardware and users through an intuitive Phoebus
CSS GUI. Extensions are being developed to the original
HKL package to handle inelastic scattering in addition tothe original elastic scattering case for neutron and X-ray
diffraction.

and energy response of sample materials. Instead of a fullcircle geometry, neutron specific facilities often use a tripleaxis goniometer with two tilt stages on top of a rotation stage
to accommodate the heavy load of magnets and cryostats.
In this work we report EPICS support for diffractometers with four and six axis of rotation in Eulerian and kappageometries for horizontal and vertical diffractometer orientations.

Figure 1: Four-circle diffractometer [3].

INTRODUCTION
Crystallography studies arrangement of atoms in a material, and inner atomic structure can be determined using
diffraction properties of penetrating radiation such as Xray, electron, or neutron. The single crystal studies use adiffractometer which allows precise rotation of the material
under study, in order to measure diffraction pattern. The
diffraction pattern identifies arrangement and symmetry of
the atoms in a crystal. In this work we report developmentof an EPICS [1] IOC that allows integration of control ofthe diffractometer rotations of the crystal under studies withbeamline controls and data acquisition typically present at
neutron and X-ray synchrotron beamlines. The integrated
controls is indispensable in order to optimize use of precious
beam time assigned at the X-ray and neutron sources.
Commercial diffractometers used at beamlines typicallyhave four or six axis of rotation (Figs. 1 and 2), but many
specialized diffractometers have been tailored to specificbeamline needs. For instance, inelastic neutron scattering [2]typically uses a triple-axis spectrometer to probe momentum∗ 1 This manuscript has been authored by UT-Battelle, LLC, under contract

DE-AC05-00OR22725 with the US Department of Energy (DOE). The
US government retains and the publisher, by accepting the article forpublication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce
the published form of this manuscript, or allow others to do so, for US
government purposes. DOE will provide public access to these results offederally sponsored research in accordance with the DOE Public Access
Plan (https://www.energy.gov/doe-public-access-plan). 2 A.B. research
was supported in part by an appointment to the Oak Ridge National
Laboratory GEM Fellowship Internship Program, sponsored by the U.S.
Department of Energy and administered by the Oak Ridge Institute for
Science and Education.
† gofronkj@ornl.gov
THPB039
706

Figure 2: Six-circle diffractometer [4].
Our EPICS control of the diffractometer consists of an
IOC that provides forward calculations (real space angle
motor to momentum), inverse calculations (momentum todiffractometer angles), and allows for scanning in inverse
space by using coordinated motion of real motors. Utilizing
the HKL C library [5], This IOC is used to factorize single
crystal diffraction angles computation for different kindsof diffractometer geometries. Integration is achieved with
PyDevice [6], which allows for communication between
Python bindings for the HKL library and EPICS Process
Variables.
The UB matrix computations use Busing & Levy [3]with two reflections. The hkl package supports simplex
computation with more than two reflections using the GSL
library. Computations are for right handed convention for
all angles, and direct space orthogonal base. The hkl libraryuses quaternions to describe diffractometer geometries and3D rotations. The library also allows for addition of custom
diffractometer geometries.
The Phoebus [7] .bob files shown in Figs. 3-8 show detailsof the EPICS control for the vertical four-circle (E4CV)
diffractometer.
THPB: Thursday Poster Session
MC4.5 Other technology

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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB040

LLM INTEGRATION INTO EPICS
Abstract
The last two years have seen a drastic rise in the usageof Large Language Models (commonly known as LLMs)
including ChatGPT, across multiple industries and applications. This has firmly established them as broadly applicable tools, proving their flexibility and power to understandand generate human-like text. In this paper, we explore
the integration of an LLM into the EPICS system. The integration will focus on using the LLM for state-of-the-art
image processing and spatial analysis of the images from thebeamlines. We aim to increase the accuracy and efficiencyof image interpretation, enabling more precise data analysis and decision-making within EPICS through the services
offered by this LLM. This integration best showcases the various potentials of LLMs in science and industry, setting thestage for future advancements in automated control systems.

ing on the advanced computational capabilities enabled by
LLMs, we plan to accomplish various improvements to thefull ease of use of the control system.

SYSTEM DESIGN
The system is entirely written in Python, forming a robust
yet flexible core for integration into EPICS. It is implemented
as a PCASpy [1] IOC, which allows for seamless integration
with the existing EPICS infrastructure. The input images
are obtained using PyEpics [2], processed through the LLM,
and the output images are then hosted with PCASpy, making
them accessible to other components of the control system.
This setup includes the implementation of a Control System Studio (CSS) page to facilitate user interaction with thesoftware’s Process Variables (PVs), providing an easy way
of controlling and monitoring the system (Fig. 1).

INTRODUCTIONEPICS is a software system that has grown out of
scientific-industrial cooperation, aiming to satisfy the emerging needs for the development of distributed control systems.
Generally, EPICS has been designed to cope with the complex control requirements of large experimental setups, suchas particle accelerators, telescopes, and other highly sophisticated scientific instruments. Its robust architecture andscalability have made it the natural choice for such applications. Moreover, it provides flexibility and efficiency inmanaging the large sets of data produced in experiments.
The core building blocks of the EPICS control system are
Input/Output Controllers (IOCs). IOCs interface directlywith the hardware and address tasks like data acquisition,
device control, and real-time processing. They are responsible for running the devices under their control, executing
commands, and gathering data from sensors and instruments.
This decentralized approach offers better scalability and fault
tolerance: each IOC operates independently while communicating with other IOCs and higher-level applications througha well-defined protocol.
The recent breakthrough in large language models, suchas ChatGPT, has enabled numerous possibilities for enhancing control systems. Large Language Models (LLMs) havetremendously succeeded in understanding human-like text
and handling complex analysis tasks, and they can easily automate many different tasks. Clearly, integrating LLMs with
the EPICS system would provide real benefits in image processing. These functionalities are key to understanding thehuge volumes of visual data that come from today’s beamlines, where exact and efficient analysis forms the foundationof the scientific approach.
This paper discusses the integration of an LLM into
the EPICS framework, specifically for image processing of
beamline images at the VULCAN beamline at SNS. BuildTHPB: Thursday Poster Session
MC4.5 Other technology

Figure 1: System Architecture Diagram showing the interaction between EPICS, CSS, and LLMs.
Upon entering the CSS page, users are presented withtwo major functions: image processing and spatial analysis.
These options cover most of the possible analytical needs,
ensuring comprehensive capabilities in data interpretationand manipulation.
The image processing function allows users to apply various transformations to input images. This includes operations such as thresholding, edge detection, image arithmetic,
and Gaussian blurring. These transformations are executedby the LLM, and the processed images are then made available as PVs for other EPICS components to access.
The spatial analysis function extracts useful information
directly from the input images. For example, it can determine
the coordinates of centroids or other features of interest. Thisdata is stored in PVs, enabling other parts of the EPICS system to leverage the insights provided by the LLM-powered
analysis.
Additionally, the system offers an online/offline mode
option. This allows users to choose how the system processes
requests based on their operational context and available
resources.
THPB040709

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E. Adams, A. Sobhani, Oak Ridge National Laboratory, TN, USA32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISSN: 2226-0366

doi: 10.18429/JACoW-LINAC2024-THPB041

CALIBRATION OF THE ANALOG BEAM-SIGNAL HARDWARE FOR THE
CREDITED ENGINEERED BEAM POWER LIMIT SYSTEM AT THE
PROTON POWER UPGRADE PROJECT AT THE SPALLATIONNEUTRON SOURCE*
C. E. Deibele†, M. Bobrek, P. Bong, K. Kasemir, K. Mahoney, C. Michaelides, Y. Tan, D. Willis
Oak Ridge National Laboratory, Oak Ridge, TN, USA
T. Allison, Osprey Digital Control Systems, Ocean City, MD, USA
C. Barbier, ITER, St. Paul-lez Durance, France
Abstract
A programmable signal processor-based credited
safety control that calculates pulsed beam power basedon beam kinetic energy and charge was designed aspart of the Proton Power Upgrade (PPU) project at theSpallation Neutron Source (SNS). The system must reliably shut off the beam if the average power exceeds
2.145 MW averaging over 60 seconds. System calibration requires pedigree in measurements, calibration
setup, and calculations. This paper discusses the calibration of the analog beam signal components up to
and including the Analog Digital Convertors (ADCs) for
implementation into the Safety Programmable Logic
Controllers (PLCs) and Field Programmable Gate Arrays (FPGAs).

BLOCK DIAGRAM
The Beam Power Limit System (BPLS) block diagramin Fig. 1 shows redundancy in the beam current measurement with two chains, each beginning with a Fast
Current Transformer (FCT) [1]. The FCTs are connected to long-haul cables that send the beam signal toan Analog Front End (AFE). Each AFE conditions thebeam signal and distributes it to two different Analog to
Digital Convertors (ADCs). One ADC is contained
within the Digital Processing Unit (DPU), which is partof the credited Personnel Protection System (PPS), andthe other is sent to the Protection System Interface(PSI) which is a Machine Protection System (MPS).

The Safety Programmable Logic Controller (PLC)
measures the beam energy through a calculation fromsix individual Direct Current-Current Transformers(DCCTs) [2] measurements. The DCCTs measure the dipole current used to steer the beam to the target station. The DCCTs are calibrated with the vendor.
One salient difference between the credited PPS system measurement and the non-credited MPS measurement is the use of timing. Timing is used in the MPS
measurement to supply a gate to measure the beam signal, while the PPS system runs independently of timing.
The following equation [3] is used to calculate thebeam charge trip limit (counts):
𝑁𝑃𝑙𝑖𝑚𝑖𝑡
𝐿𝑖𝑚𝑖𝑡 = (1 + 𝑠11 )𝑇𝐴𝐹𝐸 𝑇𝑐𝑎𝑏𝑙𝑒 𝑍𝐹𝐶𝑇,𝑘𝐴𝐷𝐶 𝐸 ∆𝑡where 𝑠11 is the reflection looking into the ADC, 𝑇𝐴𝐹𝐸
and 𝑇𝑐𝑎𝑏𝑙𝑒 are the transmission coefficients of the AFE
and long haul cable respectively, 𝑍𝐹𝐶𝑇 is the transimpedance of the FCT, N is the number of seconds to average over, 𝑃𝑙𝑖𝑚𝑖𝑡 is the threshold power, 𝑘𝐴𝐷𝐶 is thevolts/count conversion of the ADC, E is the energy ofthe beam, and ∆𝑡 is the sample rate of the ADC. This
results in Limit being in units of counts, which is provided to the DPU and PSI where the beam charge algorithms and trip comparisons are implemented in Field
Programmable Gate Arrays (FPGAs).
For the purpose of this paper, the FCT transimpedance, long-haul cable transmission, AFE transmission,and ADC conversion factor require calibration so thatappropriate trip limits can be assigned as necessary.
The quantities of the number of seconds N, the power
limit Plimit, and sample rate Δt are fixed.

FCT CALIBRATION

Figure 1: Block Diagram of BPLS.
___________________________________________* This material is based upon work supported by the U.S. Departmentof Energy, Office of Science and by UT-Battelle, LLC, under contract
DE-AC05-00OR22725† deibele@ornl.gov
THPB: Thursday Poster Session
MC4.1 Beam diagnostics

The FCT transimpedance is nominally designed to be
0.25 Ω at the factory. Parasitic elements in its manufacture add to deviations in the design value and therefore
requires to be calibrated.
To perform this calibration [4, 5], a set of coneshaped launches were designed to transition from a cable to the geometry consistent with the FCT. Figure 2
shows two launches that are assembled onto a long section of coax that is short circuited. The long coax is used
to characterize each launch independently, so that they
can be re-assembled with the FCT placed in-between.
THPB041
711

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ISBN: 978-3-95450-219-6

JACoW Publishing32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB042

Haitao Ren†, Chad Helland, Sung-Woo Lee, John Moss, George Toby, Sang-Ho Kim
Oak Ridge National Laboratory, Oak Ridge, TN, USA
Abstract
The SNS Drift Tube Linac (DTL) operates at 402.5 MHz
and consists of 6 RF tanks, DTL1 to DTL6, which accelerate the H- beam from 2.5 MeV to 87 MeV before entering
the Coupled Cavity Linac (CCL). Each DTL tank assembly has 2 sets of horizontal and vertical electromagnetic
steering magnets (24 in total) required for transverse beamsteering. The steering magnets are water-cooled copper
tubing coils designed to fit in the limited space inside thedrift tube bodies. After 20 years of operation, some of thecopper tubing steering coils have developed water leaks
likely due to elevated water flow velocities. For the leaking
coils, the cooling water has been removed and the steeringcoils have been disabled. The water leak points are inaccessible for repair so the entire drift tube will require replacement to be able to restore the electromagnet. To prepare for the possibility of drift tube replacement in the future design and fabrication of spare drift tubes is underway,
including ones with steering magnets. To simplify thesteering coil winding and avoid water leaking issues, anon-water-cooled steering magnet design has been developed. With the existing yoke, the new coils are designed to
produce the same magnetic field with lower electrical
power removing the need for water cooling. According to
the CST [1] simulations, the maximum temperature of thecoils is below 50°C with no water cooling. A prototype development is in progress and will be used for thermal testing and magnetic field verification. Details of the steering
magnet design and calculation results are presented in thispaper.

designed to fit within the drift tube bodies. This existing
design involves complex and costly winding of copper tubing and necessitates additional water-cooling circuits. Unfortunately, this design has experienced issues with waterleaks after 20 years of operations, with two incidents reported in the past a few years: one in DTL2 in 2020 andanother in DTL3 in 2023. Although these leaks did not affect the cavity pressure because they are outside the vacuum, we need to remove the water cooling and disable
these steering coils, and retore the beam operation by adjusting other beamline steering magnets. To address theseissues, a new design featuring solid copper wire magnet
without water cooling has been proposed.

EXISTING EMD COILSAs the first step of the new coils design, we developed a
CST model of the existing EMD vertical steering magnet(see Fig. 1) to calculate the field distribution as a reference.
Table 1 shows EMD magnet requirements of DTL3 as an
example in this paper.
Table 1: Required Field Strength of EMD in DTL3
Steel
Length2.88 cmGap

Current

2.83 cm

110 A

Steering
Field
560 Gs-cm

INTRODUCTION
The Spallation Neutron Source (SNS) Drift Tube Linac(DTL) tanks employ four distinct types of drift tubes to accelerate and control the H- beam [2]. Among these, the Permanent Magnet Quadrupole (PMQ) drift tubes utilize 16
permanent magnets to provide transverse beam focusingwith a gradient of 3.70 kG/cm. Additionally, some drift
tubes are empty, constructed of solid copper, while others
incorporate Electromagnetic Dipoles (EMDs) for beamsteering or Beam Position Monitoring (BPM). Each DTL
tank assembly has 2 sets of the “x” and “y” EMD steering
magnets. Two Drift tubes downstream of the EMD Drifttubes house a BPM, which will provide beam location
feedback [3].
The current EMD magnets feature a carbon steel yoke
and water-cooled copper coils encapsulated in epoxy,___________________________________________* ORNL is managed by UT-Battelle, LLC, under contract DE-AC0500OR22725 for the U.S. Department of Energy. This research was supported by the DOE Office of Science, Basic Energy Science,
Scientific User Facilities.
† renh@ornl.gov
THPB: Thursday Poster Session
MC3.6 Room temperature structures

Figure 1: CST model of the DTL3 EMD magnet.
THPB042715

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DRIFT TUBE LINAC (DTL) STEERING MAGNETSREPLACEMENT DESIGN AT SNS*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB043

Content from this work may be used under the terms of the CC BY 4.0 licence (© 2024). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

USING TimePix3 DETECTOR FOR NEUTRON AND X-RAY STUDIES*
Kazimierz J. Gofron†
Spallation Neutron Source and High Flux Isotope Reactor,
Oak Ridge National Laboratory, Oak Ridge, TN, USA
Abstract
The 65k pixel TimePix3 chip with ToA of 1.5625 [ns]nominal time resolution allows for timing and imaging
studies using X-ray, neutron, and electron spectroscopies.
The EPICS ADTimePix3 areaDetector driver enables detector control and integration into a neutron beamline acquisition system. This presentation will discuss the recent
development of the detector’s integration into neutron and
X-ray beamlines and selected results.

INTRODUCTION
Here we discuss the integration of the TimePix3 detectors purchased from Amsterdam Scientific Instruments(ASI) [1] into the EPICS [2] control system. The TimePix3
detector was integrated into EPICS [2] using the areaDetector [3] framework by developing the ADTimePix3[4] driver. Using ADTimePix3, data collection with neutron spectroscopy was reported by Funama et al. [5].

Figure 1: The ADTimePix3 Phoebus [6] control window
with an image of neutron clusters.

DETECTOR
The thermal neutron detection process uses detection ofneutron fission energy in reaction with 6Li or 10B embedded in a Microchannel Plate (MCP) [4, 5]. The two stacked
MCP typically have bias voltage levels of -2500 [V], -1300[V], and -300 [V] for the front, middle, and back MCP double stack. The detector is kept at 0 [V]. The detection efficiency is dependent on neutron energy. The quad detector
has a gap between four chips, for which influence on detection is not yet currently clear. The preview image of neutron clusters is shown in Fig. 1 using the CSS Phoebus client [6].
TimePix3 requires calibration files typically provided by
the vendor (ASI). The equalization files consist of .bpc (Binary Pixel Configuration) and .dacs (DACs settings) files.
Both equalization files are loaded during the IOC boot process. The calibration files can also be loaded from the dedicated .bob screen in the “Load Files” menu. The detector
calibration is typically performed with vendor software,such as SoPhy or Accos. The quad detector calibration
shown in Fig. 2 was done with SoPhy version 1.6.5.

* This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE).
The US government retains and the publisher, by accepting the article
for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce
the published form of this manuscript, or allow others to do so, for US
government purposes. DOE will provide public access to these resultsof federally sponsored research in accordance with the DOE Public Access Plan (https://www.energy.gov/doe-public-access-plan).
† gofronkj@ornl.gov
THPB043
718

Figure 2: A four-chip TimePix3 detector equalization of
DAC level using SoPhy.
The ASI vendor provides two programs for data acquisition: SoPhy (older) and Accos (newer). Either one of these
programs can generate equalization files (Figs. 2 and 3).
ADTimePix3 allows integration of the detector into the
EPICS beamline control environment. The ASI also provides SERVAL server and detector Emulator programs.
The SERVAL connects to a physical TimePix3 detector
over 10Gb ethernet, or to a detector Emulator program. The
Emulator was very useful during the initial ADTimePix3
driver development.

Figure 3: Loading .bpc and .dacs detector calibration from
CSS screen of ADTimePix3 driver.
THPB: Thursday Poster Session
MC4.5 Other technology

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB045

M. Champion†, M. Connell, N. Evans, J. Galambos, M. Howell, G. Johns, S. Kim, J. Moss,
G. Stephens, K. White, Oak Ridge National Laboratory, Oak Ridge, USA
Abstract
The Proton Power Upgrade (PPU) project at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) has completed the installation and testing of
all project scope required to meet threshold key performance parameters (KPPs), supported beam commissioning
in June 2024, and transitioned to operations in July 2024.
Increasing the beam energy from 1.0 to 1.3 GeV required
the installation of seven additional cryomodules in the SNS
Linac along with supporting RF systems. The accumulator
ring injection and extraction regions were upgraded, a
2 MW mercury target was developed, and ancillary target
systems were upgraded to support high-flow gas injection,
mercury off-gas treatment, and ortho-para fraction control
in the cryogenic moderator hydrogen loop. Three of fourthreshold KPPs have been demonstrated, and the project isplanning for its final review in early 2025. Beam power on
the first target station (FTS) will be ramped up to 2 MW
over the next two years. Completion of the PPU project
supports increased scientific capability at the FTS and will
support operation of the second target station (STS) uponits completion. Lessons learned will be documented and a
project closeout report will be written prior to the final
closeout of the project.

INTRODUCTION
The PPU project has been underway for more than six
years since establishing the conceptual design and cost
range (Critical Decison-1, CD-1) as depicted in Fig. 1. The
upgrade increases the accelerator beam power capability
from 1.4 to 2.8 MW, provides a 2-MW-capable mercury
target for the first target station, and constructs a tunnel
extension for future connection to the second target station.
The detailed technical scope has been described previously[1], and the project status will be presented in an invited
talk at this conference [2]. The long installation outage began in August 2023 and concluded in April 2024. All remaining PPU technical components required for threshold

KPP demonstration were installed and tested during thisoutage. An external accelerator readiness review was conducted in May 2024, and authorization for beam commissioning and routine operations was granted in early June.
Beam commissioning commenced June 7th and was completed in less than one month. Neutron production for theuser program resumed July 11th as planned at 1.3 GeV and1.7 MW. Three project threshold KPPs related to beam parameters have been achieved. Demonstration of the fourth
KPP, for target lifetime, is progressing and expected to beachieved in October 2024.

Figure 1: The PPU project execution spans seven years
from CD-1 approval to CD-4 project completion review.

BEAM COMMISSIONING
PPU beam commissioning commenced June 7th, 2024,
and proceeded quickly as shown in the timeline (Fig. 2).
First up was commissioning of the Linac with seven new
PPU cryomodules. Tune-up of the SNS Linac is a well understood process, and 1.33 GeV low-duty-factor beam wasdelivered to the Linac injection dump within a few hours.
Accumulator ring commissioning began June 8th at
1.05 GeV for comparison with accelerator performance
during the final run prior to the long outage. After successfully delivering low-duty-factor 1.05 GeV beam to the ringextraction dump, the energy was increased to 1.3 GeV, andfull-energy beam was delivered to the extraction dump on
June 11th.

___________________________________________* ORNL is managed by UT-Battelle, LLC, under contract DE-AC0500OR22725 for the U.S. Department of Energy. This research was supported by the DOE Office of Science, Basic Energy Science, ScientificUser Facilities.
Notice: This manuscript has been authored by UT-Battelle, LLC, undercontract DE-AC05-00OR22725 with the US Department of Energy(DOE). The US government retains and the publisher, by accepting thearticle for publication, acknowledges that the US government retains anonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so,for US government purposes. DOE will provide public access to theseresults of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
† championms@ornl.gov
THPB: Thursday Poster Session
MC3.4 Proton linac projects

Figure 2: PPU beam commissioning was accomplished inapproximately one month from start to neutron production.
1.7-MW-equivalent charge (22uC) at 1.3 GeV was circulated in the ring and sent to the extraction dump on
June 12th at low duty factor. Tuning for low beam loss
throughout the accelerator proceeded for several days, and
THPB045721

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COMPLETION OF THE PROTON POWER UPGRADE PROJECTAT THE SPALLATION NEUTRON SOURCE*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB046

G. Ciovati† 1 , A. Castilla-Loeza, G. Cheng, K. Harding, J. Henry, J. Vennekate
Jefferson Lab, Newport News, VA, USA
J. Lewis, Mechanical & Aerospace Engineering Department, Old Dominion University,
Norfolk, VA, USA
J. Rathke, TechSource, Los Alamos, NM, USA
T. Schultheiss, TJS Technologies, Commack, NY, USA1
also at Center for Accelerator Science, Physics Department, Old Dominion University,
Norfolk, VA, USA
Abstract
Conduction-cooled SRF niobium cavities are being developed for use in compact, continuous-wave electron linear accelerators for a variety of industrial applications. A
915 MHz two-cell cavity has been designed to achieve anenergy gain of 3.5 MeV. The design of the cell shape aims at
minimizing the peak surface magnetic field. Field flatness isachieved by adjusting the length of the outer end half-cells.
The higher-order mode analysis shows that absorbers are
not required for a moderate beam current of 5 mA. One of
the beam tubes has two side-ports for insertion of coaxial
fundamental power couplers. The mechanical design andanalysis were done to maintain a stress near or less than
15.5 MPa for all anticipated loading conditions. This is half
the measured yield strength and is to provide relief from
creep when the cavity is evacuated and stored with outside
atmospheric pressure.

INTRODUCTION
Superconducting radio-frequency (SRF) cavities are commonly used in modern particle accelerators to increase theenergy of a charged-particle beam. R&D projects in the last
few years have demonstrated the possibility to operate SRF
cavities cooled by commercial cryocoolers at an accelerating
gradient of up to ∼12 MV/m [1, 2].
These results may allow envisioning compact, high-power,
continuous-wave electron accelerators with energy of up
to 10 MeV for industrial irradiation applications, such aswastewater treatment, medical device sterilization and phytosanitary treatment [3, 4]. The beam power of these possible
novel accelerators has to be greater than hundreds of kilowatt, ideally up to 1 MW, to reduce the unit cost of treatment.
Given the high beam power requirements, the RF source of
the accelerator has to have a high efficiency to reduce theoperating cost of the accelerator. Commercially available
915 MHz industrial magnetrons have an electrical efficiencyof ∼90% with an output power of ∼100 kW. An ongoing
R&D project at Jefferson Lab and General Atomics is tar∗ Work supported by U.S. DOE Office of Accelerator R&D and Production

through Jefferson Science Associates, LLC under U.S. DOE Contract No.
DE-AC05-06OR23177† gciovati@jlab.org
THPB: Thursday Poster Session
MC4.8 Superconducting RF

geting to demonstration of efficient power combining frommultiple magnetrons and developing the control system todrive an SRF cavity [5].
In this contribution we present the RF design and the mechanical analysis of a 915 MHz two-cell cavity as part ofa larger R&D project aiming at developing a conductioncooled cryomodule, which includes cryocoolers, a coaxial
fundamental power coupler (FPC) and warm-to-cold beamline transitions. The number of cells was determined by
the available cryocoolers and space within a vacuum vessel
developed for a preceding project. Details about the FPC
design, done by RadiaBeam, can be found in Ref. [6].

RF DESIGN
The cavity was designed aiming to provide an energy gainof at least 3.5 MeV to a relativistic electron beam. SUPERFISH [7] was used for the electromagnetic design of the cell
shape. The shape design aimed at reducing the ratio of thepeak surface magnetic field, 𝐵p , to the accelerating gradient, 𝐸acc , while maintaining a wall angle, 𝛼, that facilitatessurface chemical and cleaning processes. The iris radius,
𝑅iris was chosen to be close to the largest possible valuethat could fit within the beamline flange used in 1.3 GHz
TESLA-type cavities, allowing the use of testing hardware
already available. The cell shape design includes a shortstraight segment, 𝐿eq , that is used as a parameter to tune thefrequency of the end half-cell. This allows using a single
die for pressing both center and end half-cells. Furthermore,
the presence of a straight section at the equator facilitateselectron-beam welding of a Nb ring for conduction cooling.
The equator radius, 𝑅eq , was used as a parameter to tune
frequency of the center half-cell. Table 1 lists the geometricparameters of the center half-cell. The equator weld-prep
is included in the cell-shape design and an arc with 2 mm
radius is used to connect the straight section at the equatorto the equator ellipse’s arc. The end half-cell is identical tothe center half-cell other than 𝐿eq = 3.1 mm.
The list of electromagnetic parameters of the 2-cell cavity
is given in Table 2. The highest 𝐵p measured on a conductioncooled Nb3 Sn-coated cavity was 50 mT, which would correspond to 𝐸acc = 13.6 MV/m and an energy gain of 4.3 MeV
for this cavity shape.
THPB046
725

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RF AND MECHANICAL DESIGN OF A 915 MHz SRF CAVITY FORCONDUCTION-COOLED CRYOMODULES ∗32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB050

Jinyul Hu†, Chang-Ki Min, Hoon Heo, Yong Jung Park, PAL, POSTECH, South Korea
Abstract
RF long-term stability (drift) is as important as RF shortterm stability for the stable operation of particle accelerators including PAL-XFEL. Increasing the performance of
LLRF itself becomes an important factor in maintaining
the long and short-term stability of the RF field. The reference tracking method applied to LLRF is effectively used
as a method of reducing the drift of the RF phase. However,this drift improvement method was not applied to the RF
amplitude. This time, the method of reference tracking was
newly expanded to improve the RF amplitude drift. As aresult of applying this new function to PAL-XFEL LLRF,
it is showing some effect in improving the RF amplitude
drift. We would like to share the progress so far.

INTRODUCTION
In the operation of an accelerator, not only short-term
stability but also long-term stability is important. In particular, in the case of sensitive accelerators such as XFELs(X-ray Free Electron Lasers), the influence of short-termand long-term stability is critical. An illustrative Fig. 1
shows a typical XFEL intensity. The left side of the dottedline is a case where long-term stability is well maintained,
and the right side is a case where long-term stability is poorand normal user service cannot be provided. Through this,it can be seen that long-term stability must also be wellmaintained. In order to do so, it is very important to improve the long-term stability of the LLRF (Low Level RF
controller) itself. We will present the improvement of thelong-term stability of the LLRF by applying reference
tracking to the amplitude as well.

Figure 1: An illustrative sketch of typical XFEL intensity
graph.

REFERENCE TRACKING METHOD
The reference tracking method is occasionally used to
improve the long-term stability of LLRF systems. There isalso the method of reference injection applied to European
XFEL [1]. Although the method is considered more accurate, it is needed to add hardware configurations, while reference tracking has the advantage of simple implementation with little additional hardware. Reference tracking is
mainly used to improve the stability of the phase.
___________________________________________† hjy@postech.ac.kr
THPB: Thursday Poster Session
MC4.4 Low level RF

Figure 2: A typical structure of a LLRF receiver.
Figure 2 is a diagram of a typical LLRF receiver. The
input RF signals are downconverted to IF signals, then theanalogue signals are converted to digital signals, and thephases and amplitudes of the RF are calculated. The reference tracking method of the phase is a method of compensating for the phase drift of other channels by using thephase variation of the reference, and can be implemented
as shown in Eq. 1.
𝐶ℎ. 𝑁 𝛷 𝑅𝑒𝑓. 𝑡𝑟𝑎𝑐𝑘

𝐶ℎ. 𝑁 𝛷 – 𝛥 𝑅𝑒𝑓. 𝛷(1)where 𝐶ℎ. 𝑁 𝛷 𝑅𝑒𝑓. 𝑡𝑟𝑎𝑐𝑘 is the compenstated phase ofnth channel, 𝐶ℎ. 𝑁 𝛷 is a phase before compensation, and𝛥 𝑅𝑒𝑓. 𝛷 is the change in the reference phase.
Similarly, the reference tracking of the amplitude can be
written as in Eq. 2. This method has been applied to the
LLRF of PAL-XFEL.
𝐶ℎ. 𝑁 𝐴 𝑅𝑒𝑓. 𝑡𝑟𝑎𝑐𝑘

𝐶ℎ. 𝑁 𝐴 – 𝛥 𝑅𝑒𝑓. 𝐴(2)

APPLICATION TO PAL-XFEL
The implemented amplitude reference tracking was applied to PAL-XFEL during the winter maintenance in 2023.
The layout of PAL-XFEL is shown in Fig. 3. PAL-XFEL isbased on a copper linac which accelerates electron bunches
to 10 GeV at a repetition rate of 60 Hz. It generates ultrastrong and short X-ray pulses in each of hard X-ray andsoft X-ray beamline for experiments. The linear accelerator(linac) of PAL-XFEL consists of a total of 51 RF stations,which are divided into five sections, named INJ, L1, L2,
L3, and L4. The amplitude reference tracking (ART) has
been applied to all 51 LLRFs and has been used to date.
Some RF stations are selected and the data comparing before and after the application of the amplitude reference
tracking are shown in Figs. 4-8.

Figure 3: PAL-XFEL layout.
THPB050
729

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EXTENSION OF REFERENCE TRACKING METHOD TO REDUCE RF
AMPLITUDE DRIFT IN PARTICLE ACCELERATORS

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HIGH-RESPONSE PLC-BASED MACHINE PROTECTION SYSTEMDEVELOPMENT AND PERFORMANCE FOR SRILAC
A. Uchiyama†, M. Komiyama, M. Fujimaki, T. Nishi, K. Kumagai
RIKEN Nishina Center, Wako, Japan
H. Yamauchi, K. Kaneko, SHI Accelerator Service, Ltd., Tokyo, Japan
Abstract
The RIKEN linear accelerator (RILAC), which is among
the injectors for cyclotrons at the radioactive isotope beamfactory (RIBF), was upgraded by installing a superconducting RILAC (SRILAC) to search for superheavy elements with element numbers 119 and above. Prior to conducting the SRILAC upgrade, the machine protection system in RILAC was constructed using simple relay circuits.
However, most of the accelerators at RIBF other than RILAC have been equipped with machine protection systems
using Mitsubishi MELSEC-Q programmable logic controllers (PLCs) since 2006. They follow a mechanism thatwas triggered an anomalous signal to drive the beam chopper to stop the beam, and are called beam interlock systems(BIS). Machine protection was required in the SRILAC
project to prevent vacuum deterioration of the superconducting cavity owing to changes in the beam envelope.
Thus, we developed an FA-M3 PLC-based system to realize a BIS with high response performance at a lower costthan conventional systems. This system was characterized
by implementing both relatively slow response and I/O requiring high response performance. For example, in thecase triggered by an anomalous signal from the electromagnet power supply, the simulation of the beam envelope
indicated that the response performance was relatively
slow, with a few milliseconds being sufficient.

INTRODUCTION
One of the injectors in the RIKEN radioactive isotope
beam factory (RIBF) is the RIKEN linear accelerator (RILAC) [1]. RILAC serves as an injector for the RIBF andprovides beams for standalone experimental courses. Experiments are underway to search for superheavy elementswith atomic numbers greater than 119, facilitated by an upgraded project. The primary upgrades to the RILAC include two significant improvements. The first is the installation of a new 28 GHz superconducting electron cyclotron
resonance ion source (ECRIS) upstream, which enhances
the beam intensity [2]. The second upgrade involves theimplementation of a superconducting linear accelerator(SRILAC) downstream of the existing RILAC cavities toboost the beam energy [3]. Because of the increased beam
intensity and energy from the upgrade, minor errors in theaccelerator components could easily cause significant
problems for the experimental equipment and the RIBF
beamline downstream of SRILAC.
In addition, issues with superconducting cavities, suchas quenching owing to vacuum deterioration caused bybeam loss, must be avoided. Therefore, the machine___________________________________________† a-uchi@riken.jp
THPB052732

protection system (MPS), a mechanism for protecting
hardware from the beam, must be more advanced. In response to these requirements, an MPS was developed tooperate SRILAC.

PREVIOUS SYSTEM
Before the SRILAC project, the RILAC interlock system
was implemented using hardware composed of mechanicalrelays. Consequently, the response performance of the previous system was not high, typically on the order of tens of
milliseconds. In contrast, at RIBF facilities other than the
RILAC, an interlock system based on the MELSEC Q-series programmable logic controller (PLC) is employed as
the MPS [4]. This system prevents hardware failurescaused by deviations in the beam trajectory from its normal
orbit by driving a beam chopper located just downstreamof the ECRIS in response to abnormal signals from components, such as power supplies, RF systems, and vacuum
systems. In addition to the beam chopper, the system outputs signals to insert the Faraday cups depending on thetype of input signal. This system is referred to as the beaminterlock system (BIS), and its response time is of the orderof 10 ms.

SYSTEM REQUIREMENT
The following system requirements have been established to develop the MPS for the SRILAC project. The
system is designed to minimize the complexity of both
hardware and software. In addition, human and machine
protection systems are clearly separated, with the core
logic of the system following the RIBF BIS. The selected
hardware prioritizes long-term maintainability. Furthermore, all stages of system development and operation are
handled by the team to facilitate system upgrades and rapid
troubleshooting. The development of the upper-level system is based on the experimental physics and industrial
control system (EPICS) channel access (CA) protocol,
which is the standard control protocol at RIBF. For example, with abnormal RF signals, the system achieves a performance that exceeds the typical response of the capabilities of conventional PLC-based system such as RIBF BIS
and drives the beam chopper.

SRILAC BIS SPECIFICATIONSController
When selecting hardware for the SRILAC BIS, the goal
was to develop and operate the system entirely within ateam, thereby ensuring long-term maintainability. Consequently, the decision was made to construct the system
THPB: Thursday Poster Session
MC4.5 Other technology

N. Sakamoto∗ , O. Kamigaito, K. Ozeki, K. Suda, K. Yamada, T. Nagatomo,
T. Nishi, Y. Higurashi, A. Uchiyama, RIKEN Nishina Center, Saitama, Japan
Abstract
The RIKEN superconducting heavy-ion linear accelerator (SRILAC) has been steadily supplying beams for superheavy element synthesis experiments since its commission
in January 2020 by addressing relevant issues. The decreasein the available acceleration voltage due to the increase in
X-rays i.e. field emission (FE) from superconducting (SC)cavities has been a major issue. However, this issue has
been mitigated via high-RF power processing (HPP). This
presentation reports on the current performance of SRILAC
and its prospects.

INTRODUCTION
The mission of the RIKEN Radioactive Isotope Beam
Factory (RIBF [1]) in Japan is to improve our understandingof the element synthesis mechanism via experiments using
intense heavy-ion beams.
In 2016, the RIKEN Nishina Center (RNC) started a comprehensive super-heavy element (SHE) research program.
The main objective was to expand the periodic table of elements by synthesizing new super-heavy elements. Afterthe discovery of oganesson (Og, Z = 118), the aim of the
SHE project was to discover elements beyond Z = 118. To
synthesize the Z = 119 element, the RNC adopted a combination of 51 V as the beam and 248 Cm as the target [2]. For
this experiment, a beam energy of 51 V = 6 MeV/u with anintensity of 2.5 pµA is required. Thus, the primary focus of
this project was to upgrade the accelerator by introducing a
SC linear accelerator to increase the final beam energy from
5.5 to 6.5 MeV/u and a SC electron-cyclotron-resonance ion
source (SC-ECRIS) to multiply its beam intensity by a factorof five (see Fig. 1).
Nishina BLD
SRC

to the newly constructed SC-ECRIS [5] and the improvement in the RILAC transmission efficiency [6], the maximum beam intensity of 5.2 pµA (duty 100%) exceeded the
project’s primary target intensity. In this report, an overview
and operation status of SRILAC and its relevant issues arepresented. Additionally, FE and vacuum leakage from input
couplers are described.

SRILAC OVERVIEWThe SRILAC layout is illustrated in Fig. 2. SRILAC comprises three cryomodules (CM1, CM2, and CM3) and a
medium-energy beam-transport line (V00, V10, V20, andV30) that connects the CMs, RILAC DTLs, and a highenergy beam-transport line. As shown in Fig. 2, CM1 andCM2 contain four SC-QWRs, whereas CM3 contains only
two SC-QWRs. Each SC-QWRs are labeled SC01–SC10
from upstream to downstream. The SC-QWR specifications
are listed in Table 1. The operating temperature was 4.5 K.
The SC-QWRs were fabricated from highly purified Nb
sheets with an RRR of 250. The inner surfaces were treatedusing a standard processing method as follows: (i) bulk etching via buffered chemical polishing (BCP); (ii) annealing(750 ∘ C, 3 h) in a vacuum furnace; (iii) light etching via BCP;
(iv) high-pressure rinsing (HPR) with ultrapure water; and(v) baking (120 ∘ C, 48 h). All SC-QWRs achieved the target
𝑄0 1×109 with 𝐸acc = 6.8 MV/m in the acceptance tests [7].
The operating frequency of the SC-QWRs was 73 MHz. The
amplitude and phase of the accelerating field could be set independently for each SC-QWR. The independent RF systemfor each SC-QWR enables the seamless tuning of the energyof the accelerated beams. The gap length was optimized for
𝛽 = 0.078.
RILAC

RRC
RIBF BLD

A1

V00

LINAC BLD

10m

SRILAC

Figure 1: Birds-eye view of the RILAC.
In 2020, beam commissioning for SRILAC was successfully conducted [3], with user beam service subsequently
starting [4]. Ar and V beams are provided for the experimentwith an energy ranging between 4.2 and 6.3 MeV/u. Owing∗ nsakamot@ribf.riken.jp

THPB053
0

CM1

A2
V00

NISHINA BLD

Beam
Floor

MEBT Top View

CM2
V11

RGA

A1

X-ray monitors

CM3
V21

Differential Pumping System

1300 mm

RILAC

CM1

A2

Beam

GARIS-III

SC-ECRISSRILAC

Liquid Helium Transfer Line

7540 mm

CM2
V11

V30

Side View

CM3
V21

V30

X-ray monitors

Figure 2: SRILAC layout.
One of the most crucial issues in beam-transport-line
design is preventing SC cavity contamination by dust transported from the room-temperature (RT) section through gas
flow owing to the vacuum pressure gradient. While the vacuum pressure level of the SC part decreases to as low as
THPB: Thursday Poster Session
MC3.3 Other proton/ion

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PERFORMANCE OF THE SUPER-CONDUCTING RIKEN HEAVY-ION
LINAC AT THE RIKEN RADIOACTIVE ISOTOPE BEAM FACTORY

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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STUDIES ON HIGH REPETITION RATE OPERATION OF SACLA WITH
X-BAND NORMAL CONDUCTING ACCELERATOR
T. Inagaki†, K. Yasutome, H. Maesaka, T. Hara, H. Tanaka, RIKEN SPring-8 Center, Sayo, JapanE. Iwai, T Ohshima, C. Kondo, T. Tomai, JASRI, Sayo, Japan
Abstract
The next upgrade plan for the XFEL facility SACLA is
to increase the repetition rate of the accelerator, which iscurrently 60 Hz, by one order of magnitude to 1 kHz maintaining the performance of the current SASE and electricity
usage. To improve the power efficiency, we choose X-bandas the radio frequency (RF) of the main accelerator insteadof current C-band. A basic design and optimization of theaccelerator are undergoing. As a testbed, we plan to introduce an X-band transverse deflector cavity to measure thetemporal distribution of the electron beam downstream of
the undulator. The development of equipment such as pulse
compressors, dummy loads, low-level RF control, which
are common to the systems for high repetition, has begun.

INTRODUCTION
The RIKEN SPring-8 Center and JASRI operate
SPring-8, the 3rd generation synchrotron radiation facility,
and SACLA, an X-ray free electron laser facility, providing
synchrotron radiation for many scientific experiments. The
upgrade project “SPring-8-II” is underway to replace theentire storage ring and obtain X-ray radiation with 100
times higher brilliance by 2029 [1]. SACLA has alreadybeen in operation for 13 years since 2011 [2]. We consider
an upgrade in the 2030s, along with the replacement of aging equipment [3]. In this upgrade program SACLA-II, theincrease in light intensity, the expansion of the wavelength
range, and the increase in pulse repetition rate are being
considered, which are strongly requested by users. To increase the light intensity, improvements to the electron gun
and bunch compression section are being considered. To
expand the wavelength range and increase the pulse repetition rate, part of the C-band (5.7 GHz) main accelerator
is being replaced by an X-band (11.4 GHz) accelerator.
For higher pulse repetition rates, superconducting RF
cavities are also being used in XFEL [4-6]. However, theuse of sup erconducting cavities requires a large amount ofliquid helium and huge cryo-plants to cool them, as well as
investments almost equivalent to building a new facility,
such as extending the accelerator length and strengthening
radiation shielding. On the other hand, in many experiments using XFEL, MHz pulse repetition rates are not necessary, and repetition rates of 1 kHz are often sufficient.
We therefore aim to increase the power efficiency of thenormal conducting accelerator by one order of magnitude
and increase the pulse repetition rate to 600 Hz - 1 kHz,
more than ten times the current 60 Hz, without increasing
power usage. This will enable high-repetition XFEL withthe current building, power, and cooling facilities. The acceleration energy can be increased by increasing the width___________________________________________† inagaki@spring8.or.jp
THPB054736

of the RF pulses, which will enable the wavelength range
to be extended to the higher energy side.
The SACLA-II project is studying each item with theaim of building a prototype in 2029. It also plans to introduce an X-band deflector cavity downstream of the BL3
undulator around 2027, combined with operational tests of
X-band RF. These are currently being designed and prototype tested [7].

SYSTEM DESIGN
Accelerator Configuration
The layout of SACLA is shown in Fig. 1. In the compact
400 m long accelerator section, a 1 ns, 1 A low-emittanceelectron beam generated by a CeB6 thermal cathode electron gun [8] is compressed to 10 fs and 10 kA in a buncher
cavity [9] and three bunch compressors (BCs), and accelerated up to 8 GeV in a high gradient C-band accelerator[10]. The electron beam, generated and accelerated at a
60 Hz repetition rate, is distributed by high-precision
kicker magnets [11] to two XFEL beamlines, BL2 and BL3,
and the injection into the SPring-8 storage ring [12]. In
BL1, the accelerator that was originally used as the SCSS
prototype accelerator [13] has been relocated and its energy
increased to 800 MeV and used for user experiments as an
EUV-FEL facility [14].
In the upgrade program SACLA-II, part of the downstream C-band accelerator will be replaced by an X-band
accelerator. As described in the next chapter, the X-band
accelerator can provide an average acceleration gradient of
42 MV/m even at a 600 Hz repetition rate, thus providing
a margin of acceleration energy. On the other hand, the remaining C-band accelerators and the S-band accelerators
are planned to remove the pulse compressor and operate atshort pulse RF to increase the repetition rate. As thischange lowers the acceleration gradient to about half of thecurrent level, we plan to compensate for the energy withthe high-gradient X-band accelerator and obtain more than
8 GeV energy at the exit of the accelerator. If the repetition
rate of the X-band accelerator is reduced to 200 Hz and theRF pulse width is increased, the acceleration gradient canbe increased to 48 MV/m. The energy of the electron beam
could be increased to 10 GeV to produce shorter wavelength XFELs.
As SACLA is currently also used as an injector ofSPring-8, it is difficult to make a large-scale replacement
work with a long shutdown period. Therefore, the X-band
accelerator will consist of a unit with a total length of 4 m,same as the current C-band accelerator, and will be replaced by several units every shutdown period. In this way,
the replacement can be carried out while the operation ofSPring-8 and SACLA continues.
THPB: Thursday Poster Session
MC4.7 Room temperature RF

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ISIS INJECTOR LINAC EMITTANCE MEASUREMENT
AND PHASE-SPACE TOMOGRAPHY
A. P. Letchford†, S. Ahmadiannamin, R. Williamson, B. Kyle
ISIS Neutron and Moun Source, Rutherford Appleton Laboratory, Harwell, Didcot, UK
Abstract
Accurate beam emittance measurement is vital for
optimizing high-intensity proton accelerators. Traditional
methods often only approximate the phase space ellipse
linearly, limiting their effectiveness. Comprehensive
analysis of phase space distribution, including
nonlinearities, is essential for better characterization. This
study focuses on the ISIS neutron spallation source, which
is being upgraded to increase beam intensity to 300
microamps while minimizing losses. We present
tomographic reconstruction and quadrupole scan resultsfor emittance measurement at the end of the ISIS injector,
showing strong alignment between measurements andsimulations.

INTRODUCTION
The ISIS neutron spallation source, a pulsed high-power
proton accelerator, generates high-intensity neutronradiation for various applications [1]. It includes a 70 MeV
injector linac and an 800 MeV rapid cycling synchrotron(RCS) [2]. A key goal for ISIS, like other high-intensity
hadron accelerators, is to minimize beam loss and radiation
activation while increasing beam power and stability.
Achieving this requires advanced diagnostics, precise
beam measurement techniques, and an accurate beam
dynamics model to optimize performance.
The High Energy Drift Section (HEDS), positioned after
the injector linac, hosts diagnostics and magnets essential
for beam characterization before RCS injection [3].
Accurate emittance and Twiss parameter characterization
at the injector linac’s end is crucial, with the HEDS setup
offering robust capabilities for these measurements
through both traditional and innovative methods.
Widely used measurement techniques include threescreen and quadrupole scans, with tomographic phasespace reconstruction becoming increasingly valuable foranalysing nonlinearities in beam phase space [4].
Algorithms like Filtered Back Projection (FBP), Algebraic
Reconstruction Technique (ART), and Maximum Entropy(MENT) facilitate phase space reconstruction from onedimensional beam profiles [5]. The MENT algorithm
stands out for its efficiency with fewer beam profile
measurements, addressing challenges related to beam loss
and magnet strength. In Computational Tomography (CT),
one-dimensional beam profiles are converted into twodimensional phase space distributions [6].
This paper details the experimental setup at ISIS,
including the quadrupole scan, three-screen monitor, and_____________________________________________† alan.letchford@stfc.ac.uk

THPB058
740

MENT-based CT method, and presents preliminary
emittance measurements and phase space reconstruction
results at the injector's output within the first diagnostics
setup of the HEDS section.

EXPERIMENTAL SETUPThe ISIS linac, operating at 202.5 MHz, includes a
Penning ion source delivering a 45-mA output, followed
by a Low Energy Beam Transport (LEBT) section with
75% transmission efficiency, achieved through threesolenoids for matching to the RFQ. The RFQ raises thebeam energy to 0.665 MeV with over 97% transmission.
The beam then enters a drift section, lacking matching
before being transferred directly to the Drift Tube Linac(DTL), where four tanks accelerate it to 70.5 MeV. Due tothe absence of an MEBT (under development for machine
upgrade), significant beam loss occurs in the first DTL
tank, resulting in 75% and 100% transmission in the firstand last three DTL tanks, respectively. However, thebeam's low energy prevents activation in this section.
Approximately 22.5 mA of the beam is transmitted throughthe DTL tanks and injected into the RCS synchrotron.
Fig. 1. shows the schematic of the injector and HEDS
section.
Our primary measurement section is in the initial part of
the HEDS injector, utilizing quadrupole magnets and wire
scanners (Fig. 2.). A beam dump is positioned between the
IPM3 and IPM4 wire scanners to minimize beam loss
during measurements, with the first three profile monitors
in use during machine physics experiments. Quadrupoles
QF1, QF2, QD3, and QF4 (highlighted in green) operated
at currents of 2.1, 6.25, 112.5, and 6.35 Amperes,
respectively. Wire scanners 1, 3, and 4 were used for thethree-screen method, while wire scanner 3 (IPM3) was
employed for quadrupole scans and tomographic phasespace reconstruction. The parameters for the beamline andits configuration are provided in Table 1.

RESULTSThe ISIS injector was modelled using Parmila andTrace-3D beam dynamics codes, with simulation results
shown in Fig. 3 and Fig. 4. Horizontal and vertical beamprofiles, measured with the IPM3 wire scanner undervarious quadrupole settings and rotation angles, arepresented in Fig. 5. Applying maximum entropy
techniques, commonly used in image processing, thetransverse phase space distributions at the injector linac’s
output were calculated and shown in Fig. 6. We used three
screen monitors and quadrupole scan procedures tobenchmark these calculations against topographicallyreconstructed phase spaces. Beam phase space ellipse
THPB: Thursday Poster Session
MC4.1 Beam diagnostics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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D. J. Dunning∗ 1,2 , P. Aden1 , D. Angal-Kalinin1,2 , J. A. Clarke1,2 , J. L. Collier3 , B. D. Fell1 ,J. S. Green3 , J. P. Marangos4 , S. L. Mathisen1,2 , B. L. Militsyn1,2 , M. D. Roper1,2 ,E. W. Snedden1,2 , N. R. Thompson1,2 , D. A. Walsh1,2 , P. H. Williams1,2 , M. D. Wilson3
1
STFC Daresbury Laboratory, Warrington, UK
2
The Cockcroft Institute, Warrington, UK
3
STFC Rutherford Appleton Laboratory, Didcot, UK
4Imperial College London, Blackett Laboratory, London, UK
Abstract
The UK is conducting a multi-stage project to analyse
the case for major investment into XFELs, through either
developing its own facility or by investing at existing machines. The project’s 2020 Science Case identified a clear
need for ‘next-generation’ XFEL capabilities including neartransform limited x-ray pulses across a wide range of photon
energies and pulse durations, evenly spaced high-repetition
rate pulses, and a high-efficiency facility with a step-change
in the simultaneous operation of multiple end stations. The
project is developing a conceptual design to meet these requirements, significantly aided by collaboration with international XFELs. It is also guided by an extensive ongoinguser engagement programme of Town Hall meetings andother activities (see https://xfel.ac.uk). Both the science requirements and the emerging conceptual design are expected
to be of general interest to the community.

INTRODUCTION
In 2019, the UK initiated a project to develop the sciencecase for a UK XFEL, which was published in 2020 [1, 2].
Subsequent exercises demonstrated the support of the UK
community and UK Research and Innovation provided funding for the next phase of the project: a 3-year conceptual
design and options analysis (CDOA), which started in October 2022. This phase includes developing a conceptual
design for a unique new UK facility, alongside examining
investment opportunities at existing facilities e.g., [3–12],both with the aim of realising ‘next-generation’ XFEL capabilities (the features of which are discussed below). By theend of the CDOA phase (October 2025), we will have:• explored a conceptual design for a unique new machine
aiming to fulfil all the required capabilities;• examined other investment options and collaborations
in existing XFELs;• updated the Science Case to feed into the process andinform future decisions;• held multiple Town Hall Meetings around the UK engaging with the user community;• investigated the socioeconomic impact of a nextgeneration XFEL.
∗ david.dunning@stfc.ac.uk

THPB: Thursday Poster Session
MC2.4 FELs

Year 1 focused on surveying the science requirements,
preliminary engagement with overseas XFEL facilities, planning the Town Hall meetings and initial conceptual design
scoping. Year 2 is focusing on producing a self-consistentdesign, identifying gaps in key physics and technology areas,
working with overseas XFEL facilities, and the continuationof Town Hall meetings. In Year 3, existing R&D activities
will continue and roadmaps to address gaps in key areas will
be defined. The CDOA report will be written, detailing thepreferred options; this will include associated costs, socioeconomic analysis, and an update to the Science Case. This
paper provides a summary of progress to date.

NEXT-GENERATION XFELCAPABILITIES

Next-generation capabilities were defined by distilling the
key messages within the Science Case, focusing on transformational future opportunities that can’t yet be delivered atexisting facilities. These have been refined through a wideranging consultation process between the science team, thefacility design team and with external experts. The Science
Case and ongoing engagement clearly set an emphasis on
both enhancing XFEL capabilities and on widening accessto such capabilities, defined as follows:• A high-efficiency facility, with a step-change in thesimultaneous operation of multiple end stations.
• Near-transform-limited operation across the entire Xray range (∼0.1 - 20 keV and ∼100 as - 100 fs). Nontransform-limited pulses from ∼20-50 keV.
• Evenly-spaced, high repetition rate pulses to match
samples and detectors (∼100 kHz - 1 MHz per FEL).
• Synchronisation/timing with external lasers to <1 fs.
• Widely separated multiple-colour X-rays to at least one
end station.
• Full array of synchronised sources: XUV-THz, e-beams,
high power and high energy lasers at high rep. rate.
• Data and computing systems matched to the demandsof high repetition rate acquisition.
• Minimal carbon footprint with minimal energy consumption for both operation and build.

NEXT-GENERATION XFEL CONCEPTTo develop a next-generation XFEL concept, we have chosen to initially assume a new-build facility at an international
THPB059
743

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THE UK XFEL CONCEPTUAL DESIGN AND
OPTIONS ANALYSIS PROJECT

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB064

F.-J. Decker†, W. Colocho, S. Hoobler, B.T. Jacobson, T. Kabana, SLAC, Stanford, CA, U.S.A.
Abstract
BPMs have been used for decades since their easy-touse absolute transverse position capability. Left signal
minus right signal divided by the sum times the radius
gives the beam position. The charge is “just” a relative
measurement and has to be calibrated (or ironed) against a
toroid signal. Even when the incoming charge variation ishigh (like 3% rms for the superconducting LCLS2), therelative variations are only 0.1%. This opens up quite someuses. Besides even small charge losses at beam restrictions
like collimators or septum magnets it has been found that
this signal is very useful in quantifying the charge loss
during a wire scan since losses of around 2% are observed.
By taking the difference of a few BPMs before and after
the wire scanners signal-to-noise levels of up to 5000 are
observed, making this method compatible to the typicalscintillator plus photomultiplier setup. This is especiallyhelpful where the first beam loss is hundreds of meters
downstream since most of the scattered electron make it
down the relatively wide bore of the superconducting
cavities. An SVD method to analyze the data independentby human judgement is discussed.

INTRODUCTIONFirst, we will investigate the BPM signals and their
sensitivity. Then we look for beam loss patterns along theaccelerator, followed by using the loss generated by a wire
scanner. Finally, we use the SVD method, which generates
distinctive eigenvectors in time and location.

BPM SIGNALS
The four BPM raw signals are processed to get the besttransverse beam position information [1, 2]. The charge or
TMIT (TransMITted number of electrons) value is the sumof all four channels. RF BPMs have only one charge related
signal making them a factor of two worse. The Cryomodules have button BPMs with a big bore which are evenworse, see Fig. 1. Beam losses at collimators in the SC
beamline are quite common. The beam is often steered
close to a jaw since many (>7) of the deferred BPMs arestill missing. This initiated the 30-times zoomed-in display
around 100±2% instead of the usual 0 to 120%.
A few individual BPMs showed much higher RMS jitter.
Some reasons were found where the signal raw waveform
was hitting the ±32000-count digitizer limit. Other BPMs
had four signals with very different waveform counts. The
cause for bad performances for some RF BPMs in theundulators are not yet identified.
___________________________________________*Work supported by U.S. Department of Energy, Contract DE-AC02-76SF00515.

† Decker@SLAC.Stanford.edu
THPB: Thursday Poster Session
MC4.1 Beam diagnostics

Figure 1: Charge Ratio along the SC (Super Conducting)linac to the SXR (Soft X-Ray) dump. After normalizing to
the “incoming” charge (average of #5 to #20), the charges
are the same within an RMS of 0.05% for the best BPMs.
The cryo BPMs are 5 times worse indicating the four linac
regions L0, L1, L2 and L3 at #3, around #25, #40 and #60.
Beam losses of at least 0.5% at a halo collimator (BPM
#100) are indicated by a step up in the RMS value.

BEAM LOSSES
Beam losses down to 0.1% can be localized with adisplay like Fig. 1. Mostly they were at collimators andseptum magnets needing steering the beam away from ajaw or some beam beta mismatch or emittance tuning. A
few times, we had losses at unexpected (and not watercooled) locations like in the BSYS (Beam Switch Yard to
the Soft x-ray line) where a sparse BPM region with bends
caused the beam to have less than 1 mm wiggle room.
Another place to watch is just three BPMs away from thefinal dump where the XTCAV (X-band Transverse
deflecting CAVity) is located.
When looking at numbers even a small loss of 0.1% is
too much at higher beam rates for the SC linac. At 10 kHz,
this loss is equivalent of a 100% beam loss at 10 Hz. The
BPM TMIT loss method has also helped to locate which
LBLM (Long Beam Loss Monitor) have a rate dependant
behaviour and therefore photon beam versus not ratedependant dark current losses.
For the Copper Linac we identified a loss location where
the holed-out mirror for the BC2 (Bunch Compressor) peakcurrent detector was slowly creeping into the beam pathcreating small losses. It was found earlier [3] that being
close to an obstruction increases the emittance to the pointthat no FEL intensity at hard x-rays is generated, even
before losses are obvious.

.
THPB064
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BEAM POSITION MONITORS (BPMS),USING THEIR CHARGE INFORMATION AT SLAC*32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB066

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AUTONOMOUS BEAM ALIGNMENT THROUGH QUADRUPOLETRIPLETS USING BAYESIAN ALGORITHM EXECUTION
R. Roussel∗ , D. Kennedy, A. Edelen
SLAC National Accelerator Laboratory, Menlo Park, CA, USA
A. Ody, E. Wisniewski, Argonne National Laboratory, Lemont, IL, USA
Abstract
A common challenge in online accelerator operations isaligning beams through a series of quadrupole magnets,
especially when in situ beam position monitors are notpresent. Accelerator operators generally use a trial-and-error
approach to solve this problem by sequentially measuring thecentroid deflection of the beam as a function of quadrupole
strengths. This is a challenging process that necessitates
dedicated effort by operational experts, requiring significant
beam time and personnel resources to configure basic accelerator operations. In this work, we use Bayesian Algorithm
Execution (BAX) with virtual objectives to autonomously
control steering magnets at the Argonne Wakefield Accelerator to center the beam through a quadrupole triplet. This
technique uses virtual objectives to reduce the number ofmeasurements needed to converge to an optimal solution,
resulting in a turn-key algorithm for finding the optimal
steering configuration for a set of accelerator magnets fromscratch.

INTRODUCTION
Effectively steering particle beams through magnetic elements is a necessary part of routine accelerator operations.
Beams that travel off-axis through magnetic elements, suchas quadrupoles or solenoids, are deflected when varying thefield strength of these elements due to “feed-down” effects
of multipole magnets which result in dipole fields. This
complicates automated optimization of magnetic fields asvarying the field of each magnet might cause the beam tobe further misaligned with elements downstream, such as
diagnostic screens or small apertures. Additionally, beams
that travel off-axis in magnetic elements may be subjected
to non-ideal magnetic field geometries due to fringe field effects, which can degrade beam quality. As a result, steering
beams through the center of magnetic elements is a criticalpart of accelerator operations.
Several methods have been developed to effectively determine and minimize the misalignment of beams travellingthrough magnetic accelerator elements such as quadrupole
magnets, often referred to as beam-based alignment (BBA).
In some cases, these methods use a model of the beamline
including the locations of quadrupole magnets and steering
magnets (e.g. [1]). On the other hand, other model-free approaches have been developed to determine misalignments
without the need for knowledge of the accelerator structure(e.g. [2]). However, these methods are relatively inefficient,∗ rroussel@slac.stanford.edu

THPB066
750

as multiple measurements are necessary to determine themagnitude of deflection when varying magnet strengths asa function of steering parameters.

Figure 1: Simple example beamline of alignment througha quadrupole focusing triplet. Two steering / trim magnets(T1, T2) are used to steer the beam through the center of two
quadrupole magnets (Q1, Q2) while measuring the beam
centroid location at a downstream diagnostic (in this case ascreen).
In this work, we introduce a technique that can be used
to correct for beam misalignments in magnetic elements inan efficient, model-free way. This technique utilizes recent
developments in Bayesian Algorithm Execution (BAX) [3],which is a generalization of conventional Bayesian optimization algorithms [4] to optimize so-called “virtual objectives”.
We demonstrate that this technique efficiently steers the beamthrough the centers of 2 quadrupoles in a triplet configuration with little to no prior information about the accelerator
beamline, all while respecting operational constraints and accounting for measurement noise. As a result, this technique
can be incorporated into future systems for autonomous accelerator control.

BAYESIAN ALGORITHM EXECUTION
In some optimization tasks, such as beam alignment asshown in Fig. 1, each acquisition requires a secondary scan ina separate domain to calculate the objective function. Insteadof directly measuring objectives of interest, BAX builds a
Gaussian process (GP) model [5] of observables that canthen be used to compute the objective as a function of tunable parameters. To do this the parameter space is divided
into so-called “tuning parameters” which effect the virtual
objective and “measurement parameters” which are used
to compute the virtual objective to predict the dependency
on tuning parameters. The BAX acquisition function uses
these predictions to evaluate which future measurements
will provide the most information about the steering current
that leads to a minimization of the centroid deflection. An
example application of BAX is minimizing transverse beamemittances [6]. In this case, the virtual objective involves
fitting polynomials to the beam size squared as a functionof quadrupole strength using predictions from a GP model.
At FACET-II, BAX was able to match the best emittance
THPB: Thursday Poster Session
MC4.5 Other technology

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISSN: 2226-0366

doi: 10.18429/JACoW-LINAC2024-THPB068

ADVANCEMENTS IN BACKWARDS DIFFERENTIABLE BEAM
DYNAMICS SIMULATIONS FOR ACCELERATOR DESIGN, MODELCALIBRATION, AND MACHINE LEARNING
R. Roussel1 , G. Charleux2 , A. Edelen1 , A. Eichler3 , J. P. Gonzalez-Aguilera4 ,A. Huebl2 , J. Kaiser3 , R. Lehe2 A. Santamaria Garcia5 , C. Xu5
1
SLAC National Accelerator Laboratory, Menlo Park, CA, USA
2
Lawrence Berkeley National Laboratory, Berkeley, CA, USA
3
Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
4
University of Chicago, Chicago, IL, USA
5
Karlsruhe Institute of Technology, Karlsruhe, Germany
Abstract
Many accelerator physics problems such as beamline design, beam dynamics model calibration or interpreting experimental measurements rely on solving an optimization
problem that use a simulation of beam dynamics. However, it is difficult to solve high dimensional optimization
problems using current beam dynamics simulations because
calculating gradients of simulated objectives with respect
to input parameters is computationally expensive in highdimensions. To address this problem, backwards differentiable beam dynamics simulations have been developed thatenable computationally inexpensive calculations of objective gradients that are largely independent of the numberof input parameters. In this work, we highlight current andfuture applications of differentiable beam dynamics simulations in accelerator physics, such as improving accelerator
design, model calibration, and machine learning. We also
describe current collaborative efforts between SLAC, DESY,
KIT, and LBNL to implement fast, backwards differentiablebeam dynamics simulations in Python. These tools will enable unprecedented improvements in optimization efficiency
and speed when using beam dynamics simulations, leading
to enhanced control and detailed understanding of physicalaccelerator systems.

are often restricted to optimizing a handful of parameters at
once.
An alternative simulation paradigm to gradient-free simulations is so-called “differentiable simulations” , illustrated
in Fig. 1. In addition to making conventional predictions,differentiable simulations also provide the gradient of simulations with respect to input parameters. Differentiable
simulations are enabled through the use of a computational
technique known as “automatic differentiation” [2]. Computational programs, such as beam dynamics simulations, canbe broken down into a set of atomic operations (addition,
multiplication, exponentiation etc.) for which the derivative
is analytically known. Differentiable simulations track thederivative of each calculation step alongside normal computation and use the chain rule to calculate total derivatives ofsimulation outputs with respect to simulation inputs.

INTRODUCTION
Solving challenging optimization problems is critical toaccelerator design, interpreting experimental measurements,
and calibrating physics models to realistic beam dynamics.
However, current beam physics simulations can present a bottleneck in the optimization process. Most current beam dynamics simulations used in accelerator physics are “gradientfree” simulations, where only the input and output of themodel is available. This limits the applicability of powerful gradient-based optimization algorithms, such as firstor second-order gradient descent, which often outperform
optimization algorithms that do not use gradient information [1]. The only available methods for estimating gradients of gradient-free simulations is finite difference methods,
which require higher computational costs proportional to
the number of optimization parameters. As a result, optimization problems that include beam dynamics simulations
THPB: Thursday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

Figure 1: Block diagram showing the difference between
standard programming used to model physical phenomena,
which produces outputs 𝑓 (𝑥) as a function of model inputs 𝑥,
and differentiable programming, which produces gradientsof model outputs ∇𝑥 𝑓 (𝑥) in addition to model outputs.
Several existing beam dynamics software packages [3–5]
use a technique known as “forward differentiation” [2] to calculate arbitrary order Taylor maps of accelerator elements,and more recently, to optimize accelerator design parameters
for beam dynamics under the influence of space charge [6].
However, the efficacy of this method is restricted to computing derivatives with respect to a small number of input
parameters, making it impractical for optimizing problems
that contain a large number of free parameters. On the other
THPB068
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ISBN: 978-3-95450-219-6

JACoW Publishing32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB069

T. Le†, A. Krasnykh, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
Abstract
A compact, high-voltage (HV) pulser in the nanosecond
regime for transverse electromagnetic (TEM) kickers ispresented. TEM kickers are electromagnetic deflectors
used in particle accelerators to redirect bunches of particles
out of their original trajectory into a new path, such as alternate beam paths, detectors, or other instrumentation devices. The circuit proposed in this design consists of two
main portions: a gate driver and a HV switch. The gate
driver consists of an isolated and high-speed gate driver,powered by an isolated DC/DC converter with dual output
voltages. The HV switch portion was simulated in Ansys
HFSS and is composed of a SiC MOSFET, LC resonancecomponents, and specialized diodes. When switched, the
MOSFET is used to pump a high voltage into the LC circuit
and diode stack, and the ultrafast diode turnoff delivers the
final HV pulse to the resistor load. Careful layout techniques were implemented for the MOSFET driver to reduce pulse to pulse instability.

BACKGROUND
All particle accelerators require some form of electromagnetic deflector mechanism to redirect, or kick, particle
bunches from their original trajectory into a new path, typically for alternate beam paths, detectors, or other instrumentation devices [1, 2]. These kickers must quickly reachthe desired field, maintain that field for a certain time, andthen quickly return to zero field. Thus, the drivers need topump the required current into the kicker impedance, andtherefore must operate with nanosecond rise and fall times,
adjustable pulse top durations, fast repetition rates, and low
jitter. This paper will focus on the design of the driver portion of the TEM kicker consisting of a HV Silicon Carbide(SiC) MOSFET, isolated high-speed gate driver, and an
isolated DC/DC converter.

SIC MOSFET CHARACTERISTICS
Compared to their Silicon (Si) counterparts, SiC
MOSFETs have different intrinsic material characteristics,
summarized in Table 1 [3]. The greater bandgap energy andcritical electric field breakdown means higher voltage operation and lower leakage current. Their faster saturation
velocity means faster switching and lower power loss, andtheir better thermal conductivity means better thermals,leading to a smaller die for the same temperature rise. One
downside to SiC is their lower electron mobility, whichmeans a higher channel resistance that requires a higher
gate drive voltage. These differences make SiC MOSFETS
the preferred choice over Si in drivers for kicker designs.

Table 1: Comparison of Intrinsic Material Properties of
SiC and Si MOSFETs
Property

Definition

SiC

Si

EG [eV]EC [MV/cm]
Vs [×106 cm/s]µe [cm2/V×s]
λ [W/cm×K]

Bandgap Energy
Critical Electric Field
Saturation Velocity
Electron Mobility
Thermal Conductivity

3.2
2.2
20
950
3-4

1.12
0.25
10
1350
1.5

GATE DRIVER FOR HV SIC MOSFETS
For this TEM kicker design, a high voltage is required tobe supplied to the LC circuit and diode stack that supplies
the final HV pulse to the resistor load. Due to the large
voltage at the drain of the SiC MOSFET and fast switching,
an isolated gate driver is needed to isolate the low-voltage
circuitry from the high voltage and to enhance the common-mode transient immunity (CMTI) from high dv/dt.
Two common methods for implementing isolation in gate
drivers are galvanic and optical isolation.
Galvanic isolation uses a transformer to transmit the gate
drive signal across an air gap. The signal that is applied on
the primary winding creates a magnetic field in the core,
which induces a corresponding voltage on the secondary
winding. The main benefits of using galvanic isolation are
low propagation delay and not needing any additional bias
circuitry. However, the main drawbacks are its relatively
larger size and potential for overshoot or ringing on thesecondary due to parasitics and large leakage inductance.
Optical isolation uses an LED and phototransistor totransmit the gate drive signal across a barrier. The drive
signal is applied to the LED, and the phototransistor converts the received light signal into a corresponding current.
This signal is then usually buffered by a CMOS circuit toprovide the final gate drive output. Compared to galvanic
isolation, the drawbacks are its larger propagation delay
and need for bias circuitry. However, the primary benefitsof a smaller footprint, minimal parasitics, and lack of overshoot or ringing on the output is critical for TEM kickers.

PROPOSED GATE DRIVER DESIGN
A simplified schematic diagram of the proposed designof a HV SiC MOSFET gate driver for TEM kicker is shownin Fig. 1. For the HV SiC MOSFET, Microchip’s
MSC080SMA330B4 was selected due to its high voltage
breakdown of 3.3 kV and lower total gate charge across thegate-to-source voltage range when compared to other alternatives with that high of a breakdown voltage.

___________________________________________* Work supported by U.S. DoE contract DE-AC02-76SF00515.
† thile@slac.stanford.edu
THPB: Thursday Poster Session
MC4.5 Other technology

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A COMPACT, ULTRAFAST HIGH-VOLTAGE PULSER FOR TRANVERSE
ELECTROMAGNETIC KICKERS*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB070

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LCLS-II LONGITUDINAL BEAM DIAGNOSTICS
BASED ON A SHORT S-BAND DEFLECTOR ∗V. A. Dolgashev† , E. Williams, E. M. Kraft, K. M. Ratcliffe, M. Kosovsky, A. Brachmann
SLAC, Menlo Park, CA, USA
Abstract
We designed, built and commissioned a beam diagnostic
system based on a short S-band defector and a commercial
klystron transmitter. A two feet long transverse-horizontally
deflecting S-band rf structure is installed the LCLS-II postlaser-heater diagnostic beamline at 100 MeV electron beamenergy to measure the absolute electron bunch length andto allow time-resolved beam quality measurements such asvertical slice emittance and slice energy spread. The deflector is designed to produce 0.48 MeV peak kick at 300
kW of input power. The klystron transmitter, which uses acommercial solid-state modulator, is installed in the klystrongallery at the grade level. The low-level RF system is basedon Advanced Telecommunications Computing Architectureand developed in-house. We will report on the overall performance of the project, which was successfully completed,on May 31, 2024.

INTRODUCTION
The parameters of the X-ray beam generated by a linacbased Free Electron Laser (FEL) depend to a large extent
on the quality of the electron beam entering the undulators. The quality of the electron beam is determined by theperformance of the electron injector and the means of maintaining this quality through the linac. To tune and improve
the performance of the injector, we use a set of diagnostic
tools. One such tool is the longitudinal beam diagnostics,
which uses a radiofrequency deflector to create a transverse
momentum chirp on the electron beam. The beam is then displayed on a profile monitor screen located after the bending
magnet, which serves as an energy spectrometer. Therefore,
this method allows direct measurement and tuning of thelongitudinal phase space of the beam.
SLAC has a long history of developing and using rf deflectors [1, 2]. For example, the SLAC FEL LCLS [3] uses
S-band deflectors for pre-undulator and X-band deflectors
for post-undulator beam diagnostics [4, 5]. This paper describes the concept and basic approaches to LCLS-II [6]longitudinal beam diagnostics based on a 2856 MHz rf deflector. A photograph of the deflector during its field profile
measurement after tuning is shown in Figure 1.

STACAV2 SYSTEM
A 2 ft long transverse-horizontally deflecting S-band rf
structure (STCAV2) is installed in the post-laser-heater diagnostic beamline at 100 MeV to measure the absolute electron∗ Work supported by supported by the U.S. Department of Energy contract

DE-AC02-76SF00515.

† dolgash@slac.stanford.edu

THPB070760

Figure 1: STCAV2 - traveling wave backward wave rf deflector during its after-tuning microwave characterization.
The measured data shows that the rf deflector is well tuned.
bunch length and to allow time-resolved beam quality measurements such as vertical slice emittance and slice energy
spread. The main parameters of the STCAV2 system arelisted in Table 1. The commercial klystron transmitter isinstalled in klystron gallery at grade level between penetrations 1-8 and 1-9, and the cavity is installed on a table with
43.623 m from the rf gun cathode to the cavity its center.
Overview of the STCAV2 system is shown in Fig. 2.
Table 1: Main STCAV2 System Parameters [7]Parameter

Value

Unit

Beam energy
Nominal rms bunch length (100 pC)
Nominal rms vertical norm. emittance
RMS slice energy spread
Cavity length
RF frequency
RF phase stability (rms) at all f > 1 Hz
Fast rf phase-flip capability (< 8 ms)
Fast rf phase-flip accuracy
RF phase setting range
Max rf power required
Max deflecting voltage (on crest)
Max electron beam power (120 Hz)

100
1.0
0.45
1-10
60
2856
< 0.2
180
<1
360
500
0.5
4

MeV
mm
µm
keV
cm
MHz
deg-S
deg-S
deg-S
deg-S
kW
MV
W

RF System
RF deflector The STCAV2 rf deflector type is a
traveling-wave backward-wave waveguide. It is based on theoriginal SLAC’s LOLA-II structure [1, 2]. It was recently
built with improved couplers and a smaller than the original
beam pipe. The redesign of the coupler was done by Zengai
Li of SLAC in 2018. The main parameters of the deflector
THPB: Thursday Poster Session
MC4.1 Beam diagnostics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB073

Pragya Nama∗ , The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
Ashish Kumar1 , Dai Arakawa, Kensei Umemori1 , Eiji Kako, Hiroshi Sakai1 , Takako Miura1
High Energy Accelerator Research Organization (KEK), Tsukuba, Japan1
also at The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
Abstract
The prototype of cERL (compact ERL) injector coupler
experienced excessive thermal load during high power transmission in continuous wave (CW) mode operation. Hence,some modifications has been introduced in the warm sections of the coupler which includes a scheme for active watercooling for the inner and outer conductors. The material of
the warm inner conductor was also replaced from copper
coated stainless steel to pure oxygen-free copper. The highpower test results with modified warm section shows effective thermal load mitigation. For the unmodified coupler,
the warm inner conductor’s temperature reached 183°C at
27 kW power level, while for the modified coupler with active water cooling, this temperature was mere 25°C. Dueto the conduction cooling effect from the modified warm
inner and outer conductor, the temperature rise of the entire coupler was suppressed. Furthermore, high power test
was conducted using the forced convection cooling by a fan
which additionally suppressed the temperature rise of theentire coupler components. The results demonstrate the effectiveness of the implemented modifications and suggeststhat the 100 kW class high power transmission in CW mode
could be possible.

INTRODUCTION
In superconducting radio-frequency (SRF) accelerators,
input couplers transfer power from the source to the SRF
cavities. The SRF cavities have the ability to accelerate highpower beams in continuous wave (CW) mode. However,during power transmission, the coupler’s components experience excessive thermal loads, leading to potential damage.
Essentially, the configuration of accelerator to generate highcurrent beams is constrained by the power transfer capabilityof the input coupler rather than the SRF cavities.
This problem was notably encountered by the cERL injector coupler’s test stand during 100 kW power transmission in
CW mode for one minute, about 15 years ago [1]. The cERL
injector coupler, designed for power transmission in L-band
SRF cavities, achieved power transfer up to 30 - 40 kW in
CW mode at the test stand (Fig. 1(a)) [2]. However, whiletransferring 100 kW power for a minute, the coupler’s warm
inner conductor was burned due to excessive thermal load.
The temperature measurement of the warm inner conductor
shows that maximum temperature reached about 1800 C during RF transmission of 20 kW in CW mode [3]. The ANSYS∗ pragya@post.kek.jp

THPB: Thursday Poster Session
MC4.6 RF power sources and power couplers

((a))

((b))

Figure 1: (a) cERL injector coupler test stand and (b) burned
warm inner conductor by 100 kW RF transmission and temperature profile by ANSYS thermal simulation.
thermal simulation of the warm inner conductor also suggests that the expected maximum temperature near bellows
will be around 8360 C for 100 kW power transmission. The
temperature profile by ANSYS simulation and the burned
inner conductor are shown in the Fig. 1(b). To address thisissue, some modifications were introduced in the coupler’s
warm section. The high-power test with modified components were performed with and without fan. The following
sections highlight the implemented modifications and theresults of high power test.

MODIFICATIONS IN CERL INJECTOR
COUPLERThe warm inner and outer conductor of the cERL injector
coupler were fabricated from stainless steel with 20 µm copper coating. This design exhibited poor thermal conductivity,
leading to overheating and subsequent burning of the warm
inner conductor. Additionally, substantial temperature rise
was observed in the outer conductor and other components.
To address these thermal issues, modifications were implemented in the warm section of the cERL injector coupler.
The revised components are as follows:• Warm inner conductor: The inner conductor was
re-fabricated using oxygen-free copper, which significantly improves thermal conductivity. Figure 2(a) illustrates the modified inner conductor, which includes
integrated water cooling channels. These channels allow chilled water from the chiller to circulate throughthe space adjacent to the bellows.
• Warm outer conductor: The outer conductor was refabricated with added jacket on it’s outer surface. Thisjacket is designed to be filled with chilled water, as
depicted in Fig. 2(b).
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EFFECTIVE THERMAL LOAD MITIGATION IN CERL INJECTOR
COUPLER THROUGH WARM SECTION MODIFICATION

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB074

B. C. Wang, M. W. Wang, M. T. Zhao, W. Lv, Y. H. Yan, D. Wang, M. C. Wang, W. L. Liu,
X. D. Zhang, Z. M. Wang†, L. Sheng
National Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Xi’an, China
C. B Yue, Key Laboratory of Particle and Radiation Imaging, Tsinghua University,
Ministry of Education, Beijing, China
Abstract
We have designed a 4-solenoid LEBT, aiming at transporting high-current high-repetition short-pulse proton
beam to RFQ acceptance. In this paper, we present the designs of the key parameters for the LEBT dynamics and theconical scraper. The influence of the solenoid magnetic
fields and drift spaces were discussed. The performance ofthe scraper with different dimensions were compared. The
designed LEBT and scraper can significantly remove theunwanted particles and reduce the beam loss in subsequent
RFQ while maintaining a relatively high transmission efficiency.

the high-voltage power supply only needs to work for shorttime. The E×B chopper typically has small aperture andlong length. Therefore the beam should be carefully optimised before the chopper.

BEAM DYNAMICS DESIGN
The schematic of the high-current LEBT is shownin Fig. 1. The LEBT consists 4 solenoids. The first 2
sole-noids match the beam into the E×B chopper. The last
2 so-lenoids match the beam into the followed RFQ
acceptance.

INTRODUCTION
The high-current LEBT aims at providing high-current
high-repetition short-pulse proton beam for the followed
RFQ. Specifically, proton beam of 100 mA beam current,
100 ns pulse width and 40 kHz repetition frequency is required. Ion source hardly provides such high repetition
short pulse proton beam directly. Therefore, the ion source
output DC proton beam, which is then chopped into shortpulses in LEBT. The beam requirements of the LEBT isshown in Table 1.
Table 1: Requirements of the LEBTParameter

Value
+

Unit

Particle
H
Energy80
keV
Beam current
100mA(proton)
Pulse width
100
ns
Repetition fre40
kHz
quencyThe LEBT transports 100 mA proton beam, chops thebeam to 100 ns short pulse with high repetition of 40 kHz,and matches the beam into the followed RFQ acceptance.
Considering the beam power is high and the majority of thebeam need to be cut off, an E×B chopper is adopted to reduce the requirements for high-voltage power supply. The
E×B chopper consists of a bending magnet and a pair ofelectrode plate. The electric field force and the magnetic
field force are opposite in direction and equal in magnitude.
Therefore, when the high voltage electric field is on, thebeam keeps undeflected. When the electric field vanish, thebeam is chopped by the magnetic field. In the E×B chopper,___________________________________________† wangzhongming@nint.ac.cn

THPB: Thursday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport

Figure 1: Schematic of the high-current LEBT.
The parameters to be determined are from 4 solenoids
and 5 drift sections. We have optimized the basic parameters of LEBT in accordance with the practical engineering
feasibility.
Low-energy high-intensity beams are strongly influenced by the space charge force and solenoid spherical aberration [1], which are not easily calculated analytically. It
is necessary to employ multi-particle tracking, combinedwith importing the magnetic field distribution of the solenoid, to evaluate the impact of various design parameters.
Besides, each design parameter was evaluated by the proportion of particles within a specified emittance range
when the same Twiss parameters at the RFQ entrance areachieved by adjusting the four solenoids.
Considering that the electric field of the chopper will destroy the space charge neutralization, the chopped 100 ns
beam is not sufficient to establish space charge neutralization. Therefore, the space charge neutralization rate of thebeamline before the chopper is set to 0.85, and the one forthe chopper and afterward beamline is set to 0 in simulations. The neutralization rate used in simulations is a conservative estimation [2, 3].
Simulations were conducted to investigate the influenceof the magnetic field distribution of LEBT solenoids andthe length of each drift sections on the matching efficiency.
The field distribution of the solenoid has a significant influence on the matching efficiency, and its field distribution along the z-direction can typically be expressed as:𝐵𝐵 𝑧|𝑧⁄𝑑 |
1
The one-dimensional field distribution corresponding
to different values of n is shown in Fig. 2. The larger thevalue of n, the sharper the edge of the field distribution.
THPB074
767

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DESIGN OF A HIGH-CURRENT LEBT

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA

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ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB076

THE PIP-II DEDICATED RADIO FREQUENCY PROTECTION
INTERLOCK SYSTEM FULL SCALE PROTOTYPE DESIGN AND
INTEGRATION∗
W. Cichalewski† , P. Amrozik, G. Jablonski, W. Jalmuzna, R. Kielbik, K. Klys, R. Kotas,
P. Marciniak, B. Pekoslawski, W. Tylman, Technical University of Łódź,Department of Microelectronics and Computer Science (DMCS), Łódź, Poland
J. Holzbauer, N. Patel, P. Varghese, Fermi National Accelerator Laboratory, Batavia IL, USA
Abstract
The Radio Frequency Protection Interlock (RFPI) system
watches over fifty signals near the superconducting cavities cryomodule. Its major role is to recognize faulty situations instantly and drop permits for the Low-Level Radio
Frequency control system (LLRF) and solid-state amplifier(SSA) operation. The full-scale prototype RFPI is a recent
version of the PIP-II dedicated system capable of fulfilling
the requirements of this newly constructed Linac project. Its
hardware structure is compact but still modular. It provides
enough capability to protect four superconducting resonatorsand their close environment at the same time. This worksummarizes the production phase and the integration process of this designed RFPI system. The work introduces
also the hardware and software structures of this system.
Moreover, we also summarize the on-the-bench testing experiences from the individual hardware module verificationand integrated RFPI studies.

INTRODUCTION
The newly designed and under construction linac named
Proton Improvement Plan II (PIP-II) is located in Fermilab [1]. This significant upgrade to the existing accelerator
infrastructure will allow for new scientific studies withinsuch projects as, for instance, Deep Underground Neutrino
Experiment (DUNE) [2].
This design and construction triggered the need for thedevelopment of existing and new accelerator systems. An
example of such a system is the RFPI. Its main role is to protect the RF system in case of faulty cavities and cryomodule
behavior or state. This goal can be achieved by instantaneous
operation permits dropping while monitored signals begin
to deviate from predefined safety limits. The PIP-II versionof the RFPI system must provide enough channels to protect
four cavities from a single cryomodule independently.
The first phase of the system design has resulted in the
proof of concept prototype preparation [3]. That device provided valid information on the correctness and performanceof each input/output signal. The second prototype covers afull list of input and output signals. Its structure changed in∗ Work supported, in part, by the U.S. Department of Energy, Office of

Science, Office of High Energy Physics, under U.S. DOE Contract No.
DE-AC02-07CH11359.
† wcichal@dmcs.pl
THPB076770

ternally on the hardware and software level. Still, protection
functionality for 4 cavities remained unchanged.
This design consists of one central HW unit (carrier module) that hosts the system-on-chip module responsible formain protection logic realization and the other SOM responsible for the overall RFPI management. Additionally, it
carries 7 FMC (FPGA Mezzanine Card) slots to be used formodules dedicated to different input/output signals. Suchmodularity provides possibility of different system configuration depending on the individual implementation requirements.

MAIN LOGIC UNIT AND MANAGEMENTSUBSYSTEM CARRIER MODULE (KC)Main logic unit is a FPGA based hardware module thatcollects all the input signals (in digital representation) andcompare their levels against safety limits. It is also responsible for managing output (permit) signals. Moreover, via
the FMC connectors it allows individual inputs management
and configuration (see Fig. 1).

Figure 1: FMC/KRIA carrier module.
The management processor is responsible for: individual
system modules power management, voltages and currents
monitoring, resetting KRIA SOM, providing UART interface to the main (KRIA carrier) logic, and providing the
JTAG access to KRIA chip.

FMC MODULES
The list of input and output signals required for the
full-scale design RFPI system includes more than 60 elements (based on the current specification). To cover all
THPB: Thursday Poster Session
MC3.2 Ion linac projects

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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PARTICLE MEASUREMENT ON ALL-METAL GATE VALVE FOR
CEBAF BEAMLINE VIA LASER-BASED PARTICLE COUNTER*
M. Ge†, A.-M. Valente-Feliciano, S. Balachandran, R. Ruber, T. Powers, R. Geng
Thomas Jefferson National Accelerator Facility, Newport News, USA
Abstract
The Viton gate valves installed in the CEBAF beamline
degrade significantly after long-term operation in a radiation environment, generating numerous particles that cause
heavy contamination and increased risk of field emission.
All-metal gate valves have been proposed as a replacement
for installation in the CEBAF beamline. In this paper, we
present thorough comparison tests between the Viton gate
valves and the all-metal gate valves, including evaluationsof particle levels, aging tests of the gate valves, and analysis of the particle material.

Valve [6], as shown in Fig. 1 (b), is proposed to replace all
the Viton gate valves on the CEBAF cryomodules. Unlike
the Viton seals, the materials of this all-metal valve should
not shatter after long periods of operation under high-level
radiation. The critical metric for qualifying the all-metal
valve is that the particle level generated during valve
operation (i.e., opening and closing) should be equal to orless than that of a brand-new Viton gate valve. In this work,
we present the setup and results of particle-levelmeasurements comparing the all-metal valve and the Viton
gate valve using a laser-based vacuum particle countersystem.

INTRODUCTION
During CEBAF operation, various beamline components, such as Viton gate valves, may generate microscopic
particulates. Those that migrate onto SRF cavity surfaces
can become field emitters, causing field emission (FE) andleading to performance degradation of the SRF cavities[1-3]. Frozen gases can also activate non-field-emitting
particulates [4, 5].
The Viton gate valves (VAT 01.0 Mini UHV Gate Valve[6]) have been widely used in the CEBAF beamline. Each
CEBAF cryomodule has two Viton gate valves, one at eachextremity, resulting in approximately 190 Viton gate valvesinstalled in the CEBAF accelerator. Although the root
cause of the field emitters has not been definitively identified, one of the primary suspicions is that the Viton seals
become hardened and shattered into microparticles after
long periods of accelerator operation under a high-level radiation environment.
Viton gate valve failures have occurred many times in
the CEBAF beamline. In some cases, a small piece of theViton seal was missing. There were two instances of complete Viton gate valve failure. In both cases, the Viton seals
had hardened after over 12 years of use in cryomodules
with excessive field emission. When the Viton seals shattered, adjacent cavities became inoperable due to gas discharges. Following the failure, the operational gradient ofcryomodule 1L25 dropped from 79 MeV to 59 MeV, accompanied by a significant increase in radiation. Similarly,
cryomodule 1L26, which operated at 82 MeV before thefailure, dropped to 38-45 MeV afterward. Upon disassembly of the Viton gate valve, it was observed that the Viton
seal had shattered into numerous dark particles, as shownin Fig. 1 (a).
To eliminate the potential risk of field emission from theViton gate valve, the VAT 47.2 XHV RF All-Metal Gate____________________________________________* Work supported by DOE contract DE-AC05-06OR23177† mingqi@jlab.org.
THPB080
774

(a)

(b)
Figure 1: (a) Numerous dark particles from the Viton gate
valve after disassembly from CEBAF cryomodule 1L26;(b) Photograph of the VAT 47.2 XHV RF All-Metal Gate
Valve.

LASER-BASED PARTICLE
COUNTER SYSTEM
The particle counter system was first developed at Jefferson Lab around 2018-2020 [7]. This system utilizes alaser-based vacuum particle sensor [8], capable of measuring particle sizes up to 3.6 µm and counting particles in a
2.75-inch OD vacuum pipeline in real-time. In 2022-2023,
the system was upgraded with new features, such as slow
pumping. The diagram and photograph of the particle
counter system are shown in Fig. 2 (a) and (b), respectively.
During a measurement, a gate valve is mounted above theparticle sensor. Slow pumping is performed before datacollection to prevent particle movement and agitation.
THPB: Thursday Poster Session
MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB081

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RECENT PROGRESS ON HF-FREE SURFACE TREATMENT BY
BIPOLAR PULSED ELECTROPOLISHING FOR SRF Nb CAVITIES*
M. Ge†, H. Tian, J. Musson, M. Lester, N. Brock, A.-M. Valente-Feliciano, E. Stallworth
Thomas Jefferson National Accelerator Facility, Newport News, VA, USA
Abstract
The bipolar pulsed electropolishing (BPEP) process, due
to its HF-free nature, offers a safer, more environmentallyfriendly, and cost-effective alternative to conventional
electropolishing, which uses concentrated HF and H2SO4
as the electrolyte. Jefferson Lab has developed a BPEP system that utilizes only diluted H2SO4 for the final surface
processing of niobium superconducting radio frequency(SRF) cavities. This includes single cells, 7-cell CEBAF
C100 cavities, and 9-cell TESLA-style cavities.
In this report, we present recent progress for BPEPtreated single-cell cavities at Jefferson Lab. Notably, one
single-cell cavity, following a 120°C bake, achieved an accelerating gradient (Eacc) of 37 MV/m with a quality factor(Q0) exceeding 1×10¹⁰ at 2 K. This result demonstrates thepotential for the BPEP process.

INTRODUCTION
The bipolar pulsed electropolishing (BPEP) techniquefor niobium superconducting radio frequency (SRF) cavities was patented by Faraday Technology, Inc., throughcollaborative SBIR work with Jefferson Lab [1-3]. Previous studies by Cornell University, in collaboration with
Faraday, reported that a 1.3 GHz TESLA-shaped 9-cell Nb
SRF cavity treated with BPEP achieved an accelerating
gradient of 35 MV/m [4]. Additionally, developments at
Jefferson Lab have demonstrated the successful commissioning of its own BPEP setup for 1.3 GHz single-cell andmulti-cell Nb cavities [3, 5].
BPEP uses an HF-free electrolyte and employs a novel
approach to treat Nb SRF cavities. An anodic pulse anodizes the Nb surface to form Nb oxides, while intervening
cathodic pulses mechanically erode the oxide layer throughthe action of hydrogen gas bubbles formed at the niobium
surface via electrolysis.
Systematic studies on Nb samples have demonstrated
that the removal rate and uniformity can be finely controlled using this method [3, 5]. The studies indicate thatthe removal rate of BPEP is proportional to the pulse repetition frequency (PRF). When the PRF is set at approximately 60 Hz, the BPEP removal rate is comparable to thatof conventional EP, i.e., ~0.25 µm/min [5]. Conventional
EP can lead to the formation of sulfur particles, in the formof sulfate and/or sulfite, on the niobium surface when using
aged electrolyte with a 1:10 volume ratio of HF (49%) andH2SO4 (98%) [6]. These sulfur particles can act as fieldemitters, thereby limiting the RF performance of SRF cavities. In contrast, BPEP typically employs a lower concentration of H2SO4 (37% or less) and uses mixed metal oxides

as the counter electrode, which exhibit a low overpotential
for the hydrogen evolution reaction, approximately 2050 mV at a current density of 10 mA/cm² in acidic media[7]. Consequently, BPEP significantly reduces the likelihood of sulfur particle formation on Nb surfaces [8]. Furthermore, the HF-free nature of BPEP offers substantial environmental benefits and is more cost-effective than othersurface processing methods.

BPEP SYSTEM AT JLABA BPEP system has been implemented at Jefferson Lab
and applied to various SRF cavities, including single-cellcavities, 1.5 GHz 7-cell CEBAF C100 cavities, and
1.3 GHz 9-cell TESLA-shaped cavities. This system utilizes a recently upgraded pulser system [9] that enables anadjustable PRF and operating voltage. It offers potential
improvements in surface removal for different types of
SRF cavities. Figure 1(a) illustrates the schematic diagramof the Jefferson Lab patented high power pulse generator
and controller system [9]. The pulser depicted in the figure
can generate the designed pulse structures, including anodic and cathodic pulse durations, off-time, and the potentials of both anodic and cathodic pulses. Diluted sulfuric
acid is used as the electrolyte.
During the process, the oxide layer grows when the niobium cavity is at a positive potential, and the removal of
niobium oxides occurs when the cavity alternates from a
positive to a negative potential, thereby removing the niobium pentoxide formed. Figure 1(b) shows the setup for a
1.5 GHz 7-cell CEBAF C100 Nb SRF cavity inside aclosed chemical cabinet, which is equipped with ultrasonicthickness gauges and thermocouples for in-situ monitoringof material removal and temperatures.
In order to evaluate the improved BPEP system, a seriesof comparative tests were performed between BPEP andconventional horizontal EP (HEP) using two 1.3 GHz
TESLA-shaped single-cell Nb cavities, RDT-13 and RDT5. Initially, both cavities underwent surface resetting
through HEP, followed by further surface removal using
BPEP. Vertical tests were subsequently carried out after
each removal to assess RF performance. Comparable or superior RF performance achieved after BPEP, relative to
HEP, would validate the successful development of the
BPEP system at JLab. This study highlights BPEP’s potential as a viable and effective surface processing techniquefor SRF cavities.

____________________________________________* Work supported by DOE contract DE-AC05-06OR23177† mingqi@jlab.org.
THPB081778

THPB: Thursday Poster Session
MC4.8 Superconducting RF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB084

A. B. Kavar†, S. Kashiwagi, T. Muto, H. Abiko, F. Hinode, K. Kudo, I. Nagasawa, K. Nanbu,
K. Shibata, K. Takahashi, H. Yamada, H. Hama
Research Centre for Accelerator and Radioisotope Science, Tohoku University, Sendai, Japan
Abstract
Superconducting Radio Frequency (SRF) technology is
a proven solution for generating high-power electron
beams (EB), suitable for tasks like purifying wastewaterfrom challenging impurities such as PFAS. This study elaborates on effectiveness of EB treatment and outlines design
considerations for a 1.3 GHz SRF linac operating at 5 MeV
with an average beam current of 10 mA. Numerical analyses for the accelerator system, ensuring that the beamreaches 5 MeV with the desired characteristics, lead to acompact beamline structure. This structure includes a
100 kV thermionic gridded electron gun, a 1.3 GHz 3-celllow beta buncher cavity, and three 2-cell 1.3 GHz accelerator cavities, along with necessary focusing solenoids, allfitting within 3 meter. Given the need for high beam current, achieving a high bunch repetition rate is important.
We therefore will employ the RF gating to the grid of theelectron gun. The results of the numerical studies will bepresented at this conference.

INTRODUCTION
Increased population and their rising demands for improved living standards have spurred significant industrial
advancements. This progress has led to the generation ofnumerous new impurities, among which per- andpolyfluoroalkyl substances (PFAS) stand out due to theircarbon-fluorine (C–F) bonds. These bonds impart exceptional chemical and thermal stability resulting in theirwidespread use in various applications. However, their persistence in the environment—evident from their detection
in soil, water, and human blood globally—has highlighted
the urgent need for effective methods to decompose andremove these chemicals from the environment.
To address the challenge of PFAS remediation in water,
several technologies are employed. One promising approach is Electron Beam (EB) technology [1], which has
shown efficacy in neutralizing such stubborn pollutants.
However, effective PFAS treatment requires high dosagesof EB, necessitating the development of high-power accelerators. Our research is centred on utilizing superconducting radio-frequency (SRF) technology to create a compact,
high-current electron linear accelerator. In collaboration
with KEK and the National Institute for Material Science(NIMS) in Japan, we are developing Nb3Sn SRF cavities
and designing an electron gun and buncher cavities at Research centre for accelerator and radioisotope science___________________________________________* Work supported by pioneering research support project by Tohoku
University, Japan† kavar.anjali.bhagwan.r4@dc.tohoku.ac.jp
THPB: Thursday Poster Session
MC2.5 Industrial and medical accelerators(RARiS), Tohoku University. We aim to develop a reliable
and compact electron linac system that produces short electron bunches with minimal complexity and cost, utilizing a
DC high voltage thermionic cathode for high current density and ease of maintenance.

EB WORKING
EB treatment [2, 3] is unique in that it produces highly
oxidizing and reducing species simultaneously as shown in
the Eq. (1) with the capability of generating these species
higher than any other hydrolysis method.
H O ⎯⎯⎯⎯⎯e , •OH, •H, 𝐻 𝑂 , H , H O(1)Interactions of these species with impurities in waterlead to the degradation of the contaminants. PFASs [4, 5]also after EB irradiation decomposes on interaction withthese species as given in the Eq. (2).
C F SOEB →C F•
𝑢𝑛𝑠𝑡𝑎𝑏𝑙𝑒𝑃𝐹𝑂𝑆

SO•
(2)

⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯•

C F
𝑢𝑛𝑠𝑡𝑎𝑏𝑙𝑒 𝑃𝐹𝑂𝑆

HF

The reaction chain continues to further cleave the C-F
bonds reducing PFAS into less toxic and simple compounds. The destruction of PFAS by cleavage of these C-F
bonds require doses of more than 100 kGy [1]. EB accelerator having the ability to provide 100s of kGy make EB
treatment a practical and sustainable alternative for PFAS
and wastewater treatment.

DESIGN & PARAMETERS
To design the accelerator for environmental applications, we need to set parameters such as beam energy andbeam current. Specifically, the beam energy must be below
10 MeV to avoid inducing radioactivity in water. Additionally, lower energy levels allow for a smaller and more costeffective accelerator. However, the penetration depth ofelectrons in water decreases with lower energy [6] asshown in the Fig. 1, complicating the construction of aneffective irradiation system. Therefore, we chose a beamenergy of 5 MeV, striking a balance between being neither
too high nor too low. For beam current, there is no upper
limit, but the achievable beam current is constrained by theavailable power coupler. As an initial target, we aim for a
THPB084
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NUMERICAL STUDY OF 5 MeV SRF ELECTRON LINAC FORWASTEWATER PURIFICATION*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB085

S. Kashiwagi†, A. B. Kavar, K. Shibata, H. Abiko, F. Hinode, H. Hama, K. Kudo, T. Muto,
K. Nanbu, I. Nagasawa, K. Takahashi, H. Yamada,
Research Center for Accelerator and Radioisotope Science, Tohoku University, Sendai, JapanK. Umemori, H. Sakai, H. Ito, T. Yamada, S. Shanab, KEK, Tsukuba, Japan
A. Kikuchi, S. Ooi, M. Tachiki, S. Arisawa, NIMS, Tsukuba, Japan
Abstract
Various radioisotopes (RIs) are used in the field of nuclear medicine for diagnosis, such as PET and SPECT. In
recent years, RIs are applied to therapy of cancer and theactinium-225 has been confirmed to be effective in thetherapy of advanced cancer. One of the promising RI production methods for medical application is the use of highintensity beam in accelerators. In the case of an electron
accelerator, a photonuclear reaction is used in the RI production process. We have started research and developmentof a 4K niobium-tin (Nb3Sn) superconducting RF (SRF)
electron accelerator system for RI production, which canbe operated with a compact conduction cooling system anddoes not require a large-scale cooling system. As a firststep, we plan to develop a single-cell Nb3Sn superconducting cavity and a cryomodule, and to demonstrate its performance by beam acceleration experiments. In this presentation, we report the basic design of the SRF electron linear
accelerator (linac) and R&D of Nb3Sn SRF cavity.

INTRODUCTIONRadioisotopes (RIs) are widely used in nuclear medicine
for nuclear diagnosis. In recent years, the use of RIs for
medical use has taken a new development from diagnostics
to therapy, as evidenced by the confirmation of the efficacy
of RI-based internal therapy (Radionuclide Therapy, RNT)in therapy for cancer. In particular, the radionuclide therapy
using actinium-225 (225Ac), an α-emitter RI, is attracting
worldwide attention as a therapy for advanced cancer [1].
At present, 225Ac can only be produced with less than
100 GBq per year by a radioactive decay from thorium-229(229Th) at research institutes in Germany, the U.S., and Russia. Three times doses of nuclear pharmaceuticals for one
patient requires 20 MBq of 225Ac, therefore, it is difficult
to deploy a full-scale radionuclide therapy worldwide at
the current production rate. Medical RIs can also be produced using nuclear reactors and particle accelerators. Advantage of accelerator-based RI production can produce
the required amount of RI when it is necessary. The 225Ac
can be produced by the reaction of 226Ra(p, 2n) 225Ac using
proton beam. The amount of production cannot be increased by using the high intensity beam or a thick target,
since the proton beam has a short range in a target material.
On the other hand, in the case of 225Ac production byphotonuclear reaction (γ, n) using electron beams, theamount of RI production can be increased by using a high___________________________________________† kashiwagi@raris.tohoku.ac.jp
THPB: Thursday Poster Session
MC2.5 Industrial and medical accelerators

current electron beam and a thick target (Fig. 1). The advantage of this method using electron beam is that there arefewer impurities (unnecessary isotopes).
To achieve mass production of medical RIs using anelectron accelerator, we have started research and development of a 4K niobium-tin (Nb3Sn) SRF electron linac capable of high-current beam acceleration. From the development of SRF cavities in the United States, it is known
that, in the case of a Nb3Sn SRF cavity, the performance(Q0) is almost equivalent to that of a bulk niobium SRF
cavity cooled to 2 K by cooling the cavity to 4 K which canbe achieved by conduction cooling [2]. Since a Nb3Sn SRF
cavity does not require a large-scale cooling plant, it is possible to construct a superconducting accelerator even insmall facilities such as universities. As a first step, we plan
to fabricate the S-band single-cell Nb3Sn SRF cavity andbuild cryomodule with a conduction cooling for the SRF
cavity. Experiments will be performed to demonstrate abeam acceleration using the Nb3Sn cavity.
In this paper, we describe the basic design of the 35 MeV
SRF linac for RI production and the demonstration of beam
acceleration using the Nb3Sn cavity.

RADIOISOTOPE PRODUCTION BASEDON ELECTRON ACCELERATOR
Bremsstrahlung γ-ray photons are generated by electron
beam injecting a heavy metal such as platinum (Pt) or tantalum (Ta). Photonuclear reactions occur when atomic nuclei are exited via the capture of incident photons and relax
by emitting one or several elementary particles or nuclei
fragments. For photon energies below 30 MeV near the Giant Dipole Resonance (GDR), that are generally used forphotonuclear production of Ris production [3].
In the production of 225Ac using an electron beam, radium-226 (226Ra) is irradiated with γ-rays to produce radium-225 (225Ra) by photonuclear reaction, and then 225Ac
is produced by its β-decay. The photonuclear reaction crosssection of 226Ra is shown in Fig. 2 [4]. For efficient RI production, a large number of γ-ray photons aroundFigure 1: Actinium-225 (225Ac) production via photonuclear reaction.
THPB085
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DEVELOPMENT OF HIGH-POWER 4K NB3SN SUPERCONDUCTING RF
ELECTRON LINAC FOR MEDICAL RADIOISOTOPE PRODUCTION

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB089

D. Hedji1, 2 † , R. E. Laxdal1, 2 , P. Kolb1 , Z. Yao1 , V. Zvyagintsev1 , T. Junginger2
1
TRIUMF, Vancouver, B.C., Canada
2
Department of Physics and Astronomy, University of Victoria, Victoria, B.C., Canada
Abstract
Superconducting Radio Frequency (SRF) technology is a
key component in many particle accelerators operating in acontinuous wave, or high duty cycle, mode. The on-line performance of SRF cavities can be negatively impacted by thegradual reduction in the accelerating gradient that can be attained within a reasonable field emission level. Conventional
cleaning procedures are both time- and resource-exhaustive
as they are done ex-situ. Plasma processing is an emerging in-situ method of cleaning which chemically removes
hydrocarbon-based field emitters through plasma. An R&D
program is underway at TRIUMF with the goal to develop
fundamental power coupler (FPC) driven plasma processing of the installed 1.3 GHz nine-cell cavities in the ARIEL
30 MeV SRF eLINAC. Processing recipes have been systematically studied in single-cell and multi-cell cavities off-line.
The progress on these developments will be reported.

INTRODUCTION
TRIUMF’s Advanced Rare IsotopE Laboratory (ARIEL)
program includes a 3 mA, 30 MeV SRF electron linear
accelerator (eLINAC) operating in continuous wave (cw)
as a driver to produce radioactive ions through photofission [1,2]. The eLINAC consists of three 1.3 GHz ninecell ARIEL cavities housed in two cryomodules; one within
an “injector” module, and the remaining two residing in an“accelerator” cryomodule. Each cavity is specified to operate
at a minimum accelerating gradient of 10 MV/m to achievea threshold Rare Isotope Beam (RIB) production energy of
30 MeV.
The yield of the photo fission process is highly dependent
on the electron energy, as seen in Fig. 1. Reductions in thecavity gradient significantly decrease RIB yield and must be
avoided. Particulate contamination therefore poses a serious
concern for operational efficiency. Field emitters reduce cavity performance through local heating effects and radiation
emission, degrading the quality factor of the affected cavity.
Various techniques have been developed to mitigate fieldemission, but each suffer from some intrinsic limitation. Either large resource and time allocation is needed as they aredone ex-situ, or they are insufficient at removing hydrocarbon contamination. Plasma processing is an in-situ cleaning
technique that has been demonstrated to be effective for anumber of linac facilities [4,5,6]. Plasma processing utilizes
a mixture of an inert gas (i.e. helium or argon) and a reactive
gas, oxygen, in the form of a glow discharge to chemicallyclean the inner cavity surface.
THPB: Thursday Poster Session
MC4.8 Superconducting RF

Figure 1: Photo-fission production rates as a function ofelectron energy for the ARIEL target stations [3].
TRIUMF is pursuing plasma processing for application at
the eLINAC to derisk the potential of field emission reducing the available gradient past a point in which RIB yieldis compromised. However, ignition through Higher Order
Mode (HOM) couplers used in other applications of plasma
processing cannot be directly applied on our current configuration. Specifically, the ARIEL cavities are a unique variantof the TESLA design, with modified end groups equippedwith two FPCs each. HOM dampers are also utilized at the
upstream and downstream beam pipe locations to absorb
HOMs [7]. For this reason, we are exploring plasma ignition using FPCs in the TM010 passband. In this paper, we
will report on our developments in single-cell and multi-cellstructures.

METHODS
The apparatus is shown in Fig. 2. A gas supply system
continuously injects the process gasses into the cavity, while
a pumping system is used to remove byproducts from theplasma reaction. In addition, an RF system is used to excite
the cavity fields to strike a plasma at a mode-dependent
location. Figure 3 shows an example of a plasma generated
within a 1.3 GHz single-cell cavity using this setup.

Gas Supply System
As part of our early studies we have chosen helium as theinert support gas. The gas supply system manages the gas
flow within the cavity environment. Gas injection is doneusing a series of shutoff and leak valves to regulate the percentage of helium gas to oxygen gas, keeping oxygen levels
within the range of 5–10%. Total gas pressure within thecavity is measured using a CDG-500 capacitance diaphragm
gauge such that total pressure can be regulated to be within
the range of 80 mTorr to 200 mTorr.
THPB089
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DEVELOPMENT OF PLASMA PROCESSING OF 1.3 GHZ
SUPERCONDUCTING RADIOFREQUENCY CAVITIES AT TRIUMF

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB091

Y. Ma †, K. Fong, P. Kolb, R.E. Laxdal, R. Leewe, K. Piletskiy, V. Zvyagintsev
TRIUMF, Vancouver, BC, Canada
Abstract

TEST PROGRESS

Now the stage of the 30 MeV portion of ARIEL (TheAdvanced Rare Isotope Laboratory) e-Linac (1.3 GHz,
SRF) is under commissioning which includes an injector
cryomodule (ICM) with a single nine-cell cavity and the 1staccelerator cryomodule (ACM1) with two cavities configuration. This paper is focused on the recent advances towards high power operation which includes ICM MRO ande-gun tuner upgrade, PID loop test, continuous operation
test.

INTRODUCTION
ARIEL e-Linac is a continuous-wave (CW) superconducting electron linear accelerator. The ‘Demonstrator’
phase of ARIEL was installed for initial technical and beam
tests with successful beam acceleration to 22 MeV [1]. The
ACM1 cryomodule, initially installed with one cavity, wasthen updated to 2 cavities [2] but still driven by a single
klystron in vector sum as shows in Fig. 1. 30 MeV beam
has been achieved after ACM1 which energy gain is about
20.6 MeV [3, 4].

ICM MROThe ICM cavity experienced a significant degradation in
Q0 due to pollution from venting and pumping. In 2016, theRF space of the ICM was vented too fast. Additionally, a
10 Torr pressure step occurred during pumping, increased
the problem, particularly when the pressure dropped from716 Torr to 708 Torr while the cavity was on the lower side.
Figure 2 illustrates the impact of these events. After the
event, the cavity couldn’t operate at 10 MV/m due to strong
field emission. After pulse conditioning, it became possible
to run at 10 MV/m, though this was accompanied by strong
x-ray emissions and a reduced Q0 factor, around 4 × 109.
To prevent such operational errors, a slow pumping andventing system has been developed and implemented foreach cryomodule. The ICM cavity was later refurbished ina clean room and pumped with slow venting/pumping system on beamline. The test results show successfully restoring its performance to a Q0 factor of 1 × 1010 at a 10 MV/m
gradient.

Figure 2: ICM Q0.
Figure 1: The present configuration of the e-Linac.
During the 2020-2021 shutdown, we made MRO for the
ICM to recover performance. In 2021, 10 kW beam operation had been achieved with a 500 µA beam, using an Iterative Learning Controller (ILC) for beam loading compensation [5], and in 2023 upgraded the e-gun RF tuner. At the
beginning of 2024, we successfully maintained three daysof continuous operation. Recently, to improve beam current stability due to temperature fluctuations, we implemented a PID loop for current regulation using the ACCT
signal as feedback.
___________________________________________* TRIUMF receives funding via a contribution agreement with the National Research Council of Canada.
† mayanyun@triumf.ca
THPB: Thursday Poster Session
MC2.2 Electron linac projects

Iterative Learning Controller
The e-Linac must operate at much lower power levels
during commissioning and beam development. To achievethis, the e-Linac is pulsed with varying repetition rates andpulse lengths, which results in significant transient beamloading in the SRF cavities. Especially when the beam
power ramp-up, which is accomplished by increasing theduty factor.
To improve beam loading compensation, Iterative
Learning Control (ILC) is employed in parallel with theconstant-gain feedforward controller [5] in each cryomodule LLRF. With the optimized ILC controller parameters,
it can effectively compensate beam loading with varying
repetition rates and pulse widths, as shown in Fig. 3. The
average beam power successfully reached 10 kW with acurrent of 500 µA and an energy of 30.2 MeV.
THPB091
793

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THE STATUS OF ARIEL e-LINAC RF SYSTEM*

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB092

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PHYSICAL DESIGN OF THE INJECTOR FOR XIPAF-UPGRADING∗
C.B. Yue1,2,3 , P.F. Ma1,2,3,4 , Q.Z. Xing†1,2,3 , B.C. Wang4 , C.T. Du1,2,3 , S.X. Zheng1,2,3 ,X.L. Guan1,2,3 , M.T. Zhao4 , W.L. Liu4 , M.W. Wang4 , W. Lv4 , Z.M. Wang4 , X.W. Wang1,2,3
1 Key Laboratory of Particle and Radiation Imaging, Tsinghua University, Ministry of Education,
Beijing, China
2 Laboratory for Advanced Radiation Sources and Application, Tsinghua University,
Beijing, China
3 Department of Engineering Physics, Tsinghua University, Beijing, China
4 State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Xi’an, China
Abstract
This paper describes the physical design of one linac injector for the proton/heavy ion synchrotron, which is underconstruction for Xi’an 200 MeV Proton Application Facility(XiPAF) heavy ion upgrading project. A heavy ion linac
injector will be constructed close to the existing proton linac
injector. The heavy ion injector consists of one electron cyclotron resonance(ECR) source, one low energy beam transport(LEBT) section, one radio frequency quadrupole(RFQ)
accelerator, one interdigital H-type drift tube linac(IH-DTL),
and one linac to ring beam transport(LRBT) section. Heavy
ion beams will be accelerated to 2 MeV/u. The unnormalized 99%-particles emittances at the injection point of proton and heavy ion are optimized to be lower than 10 and
16 𝜋 mm·mrad, respectively. Besides, low dispersion at
the injection point is obtained to minimize the beam offset
caused by the dispersion mismatch in the synchrotron. Three
scrapers are installed in the LRBT to meet the requirmentof emittance and dispersion.

INTRODUCTION
Xi’an 200 MeV proton application facility(XiPAF) is thefirst facility in China specifically designed to simulate spaceradiation environments. It was officially launched in 2014
and completed overall beam emission in 2020 [1–3]. XiPAF
can currently provide a stable proton beam of 20∼200 MeV,
and the on-target particle flux can reach an adjustable rangeof 105 ∼108 p/cm2 /s [3]. XiPAF is currently composed of anegative hydrogen ion linac, a medium energy beam transport line(MEBT), a proton synchrotron [4], a high energy
beam transport line(HEBT), and an experimental target station.
In recent years, the demand of heavy ion single event
effect(SEE) experiments is rapidly increasing. The XiPAFupgrading project has been proposed in order to improve
the heavy ion SEE experimental facilities. Based on the
proton synchrotron at present, a new heavy ion injector will
be constructed to provide heavy ions with a charge-mass
ratio in the range of 1/3 ∼ 1/6.5, at the energy of 2 MeV/u.
∗ Work supported by the National Natural Science Foundation of China(Grant No. U1730120 and 11975138) and the fund of the State Key
Laboratory of Intense Pulsed Radiation Simulation and Effect (Grant No.
SKLIPR2001).
† xqz@tsinghua.edu.cn
THPB092
796

The heavy ion injector consists of an electron cyclotron
resonance(ECR) heavy ion source, an low energy beam transport(LEBT), an radio frequency quadrupole(RFQ), an interdigital H-type drift tube linac(IH-DTL), and a linac toring beam transport(LRBT) section. The RFQ and IH-DTL
can accelerate heavy ions to 400 keV/u and 2 MeV/u respectively, which can meet the injection energy requirementof the synchrotron. For the proton injector, existing RFQ
and Alvarez-DTL will be reused, and modifications will bemainly made on ECRIS and LRBT.
The overall conceptual design has been completed [5],and this article mainly introduces the physical design of theentire linear injector.

REQUIREMENT OF THE INJECTOR
Because there are various kinds of heavy ions, Bi32+ ionswith the smallest charge-mass ratio are selected for heavy ion
injector optimization design. The type of proton source haschanged from the H− to H+ due to the change of injection
method from stripping injection to multiturn injection. The
requirement parameters of the injector are shown in Table 1.
The sketch diagram of the whole injector is shown in Fig. 1.
Table 1: Design Parameters of the Linac Injector
ParameterProtonHeavy ion

Injected ion
H+C4+ ∼ Bi32+
Charge-mass ratio
1
1/3 ∼ 1/6.5
Injection energy
7 MeV
2 MeV/uPeak current++
20 mA(H ,H2 ) 50 eµA(Bi32+ )exit of the ECRIS
Injected current
2∼4 mA≥17 eµA(Bi32+ )Unnorm. emit.
≤10π mm·mrad ≤16π mm·mrad
99%-particles
Momentum spread
≤0.3%
≤0.3%
99%-particles
RF Frequency
325 MHz108 MHz
Repetition rate
0.1 ∼ 0.5 Hz
0.1 ∼ 0.5 Hz
Beam pulse width
60 ∼ 100 us
60 ∼ 100 us

THPB: Thursday Poster Session
MC3.2 Ion linac projects

.IOD dna ,rehsilbup ,krow eht fo eltit ,)s(rohtua eht ot noitubirtta niatniam tsum krow siht fo noitubirtsid ynA .)4202 ©( ecnecil 0.4 YB CC eht fo smret eht rednu desu eb yam krow siht morf tnetnoC

IMPACT OF COHERENT SYNCHROTRON RADIATION EFFECTON GENERALIZED LONGITUDINAL STRONG FOCUSING
INSERTION UNIT*
Jihong Bian, Zizheng Li, Wenhui Huang†, Chuanxiang Tang
Department of Engineering Physics, Tsinghua University, Beijing, China
Xiujie Deng, Institute for Advanced Study, Tsinghua University, Beijing, China
Abstract
The generalized longitudinal strong focusing (GLSF)
scheme is a potential approach for a steady-state microbunching (SSMB) storage ring, leveraging the ultra-low
vertical emittance in the storage ring. It achieves active vertical-longitudinal coupling through an insertion unit, further compressing bunch length from the hundreds of nanometers scale in the main ring to the nanometers scale,thus emitting coherent radiation. Due to the extremely
short bunch length, coherent synchrotron radiation (CSR)
effect may significantly impact beam dynamics. We developed a particle tracking program based on one-dimensional
CSR model to preliminarily evaluate the influence of CSR
effect in the GLSF scheme under current design parameters.
Our work contributes to the future optimization of the
GLSF scheme.

INTRODUCTION

To maintain the steady-state operation, the beam must return to an uncouple and unmodulated state after passing
through the whole insertion unit. Therefore, part3 is introduced to form an isochronous and achromatic lattice, together with part2, allowing MOD2 to directly eliminate themodulation caused by MOD1 through an opposite modulation. Finally, part4 clears out any remaining vertical-longitudinal coupling effects. Note that the drastic variationsof bunch length occur in part2 and part3.
Coherent synchrotron radiation (CSR) effects become
particularly pronounced when short bunches pass throughbending magnets, potentially adversely affecting beam
quality by increasing beam energy spread and causingtransverse emittance dilution. In the GLSF insertion unit,
where the bunch length is extremely short and varies significantly, CSR effects may prevent the beam from compressing to the expected length at radiation spot. Additionally, it may also interfere with the cancellation of modulation, thereby disrupting the maintenance of the steady-state
operation. To assess the impact of CSR, we have developed
a particle tracking program that incorporates CSR effects
based on linear beam dynamics. We have evaluated and analyzed the influence of CSR in the GLSF insertion unit using the current design parameters. And we found that the
influence is acceptable for a single pass case.

Steady-state microbunching (SSMB) storage ring [1-4]is a promising solution for high average power and highpeak power extreme ultraviolet (EUV) light source. In
principle, SSMB storage rings can stably form electron
bunches with nanometer-scale lengths per revolution, capable of generating coherent EUV radiation. The generalized longitudinal strong focusing (GLSF) [5] is a possible
SSMB scheme. In the GLSF scheme, the main ring is a
low-alpha ring, where hundreds of nanometer-scale bunch
lengths are achieved using laser modulators with modulaISBN: 978-3-95450-219-6
ISSN: 2226-0366tion wavelengths much shorter than traditional
RF cavities doi: 10.18429/JACoW-LINAC2024-THPB093
32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
JACoW Publishingin conventional storage rings. The core of the GLSF
scheme is an insertion unit. Through active vertical-longitudinal coupling, this section projects the inherently ultraFigure 1: GLSF insertion unit layout.
low vertical emittance of the storage ring into the longitudinal direction, further compressing the bunches from the
SIMULATION METHOD
main ring to nanometer-scale for radiation generation. To
The theory of CSR has been extensively studied. Curachieve steady-state operation, the latter part of the inserrently,
the most commonly used model in particle tracking
tion unit decouples the bunches after radiation emission
programs
is the one-dimensional CSR wakefield model,
and returns them to the main ring.
which
treatsthe beam as a thread charge distribution. MurIn a typical layout of the GLSF insertion unit, there are
phy
et
al.
[6]
have provided a detailed description of thefour vertically dispersive lattice sections, labeled as part 1one-dimensional
steady-state CSR model. The CSR wake4, along with two laser modulators, MOD1 and MOD2, as
canbeexpressed
as:illustrated in Fig. 1. Bunch compression is achieved𝛾
through the combined action of part1, MOD1, and part2.
(1)𝑤(𝜇) =𝜙(𝜇),3𝜋𝜖 𝜌____________________________________________* Work supported by the National Natural Science Foundation of China(NSFC Grant No. 12035010)† huangwh@mail.tsinghua.edu.cn

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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COMPACT FIELD EMISSION ELECTRON GUN DRIVEN BY THz WAVE*
W. Yu, K. Peng, S. Fan, Y. Fu, L. Wang, C. Song, W. Huang†
Department of Engineering Physics, Tsinghua University, Beijing, China
Abstract
Accelerator-based light sources require high brightness
electron beams to improve performance in exploring structure of matter. Higher acceleration gradient is the key togenerate high brightness electron beams and is more feasible with higher frequency and shorter pulse length electromagnetic wave according to previous empirical formulas.
A tapered rectangle waveguide structure driven by terahertz (THz) wave is designed as a compact electron gun.
A nanotip is fabricated by focused ion beam (FIB) in thecentre to enhance the field and to emit electrons. The average emission charge per pulse is measured by a Picoammeter, and the peak value reaches 10 fC. The max electron energy beyond 4 keV is measured from the signal of channel
electron multiplier behind a -4 kV metal girds, revealingthat maximum acceleration gradient is beyond
100 MeV/m. These results indicate promising performanceof compact THz electron gun in high brightness electron
injection. Further research will be done in the future.

INTRODUCTION
Compact terahertz (THz) electron accelerators and injectors have emerged as an active research focus with the development of strong-field THz technologies, providing thepotential for high-gradient acceleration as suggested byprevious empirical formulas [1, 2]. This capability is beneficial to generating high-brightness electron bunches,
thereby enhancing the performance of accelerator-based
light sources for the investigation of matter’s structure.
THz-driven acceleration of electron beams has beenachieved with an effective acceleration gradient of
85 MeV/m and an energy gain of up to 204 keV [3]. The
electron beam emitted by THz photocathode electron gun,with a charge of approximately 10 fC, achieves a maximum
electron energy of 14 keV [4]. This corresponds to an acceleration gradient of approximately 280 MeV/m, which ismuch higher than that of an X-band photogun, yet the maximum electron energy is significantly lower. Further research is required to enhance the performance of THz accelerators and electron guns.
In this paper, we report on the setup of experimental platform for THz electron guns research in Tsinghua University. Beam experiments were carried out using the designed
compact THz field emission gun. Emission charges up to
10 fC were obtained with the maximum energy detectedexceeding 4 keV. This corresponds to an acceleration gradient over 100 MeV/m, which was limited by our available
THz pulse energy. Despite the limitation, it shows promising high-gradient acceleration capabilities.

Figure 1: The schematic layout of the experiment.
____________________________________________* This work is supported by National Natural Science Foundation of China(NSFC Grant No. 12035010).
† huangwh@mail.tsinghua.edu.cn
THPB094804

THPB: Thursday Poster Session
MC1.2 Electron and ion sources, guns, photo injectors, charge breeders

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB095

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DESIGN AND SIMULATION OF VIRTUAL PEPPER-POT METHOD FOR
LOW ENERGY PROTON BEAM
E. Cosgun∗ , M. S. Hur, Ulsan National Institute of Science and Technology, Ulsan, South Korea
S. Moon, D. Kim, Korea Multipurpose Accelerator Complex, Gyeongju, South Korea
M. Chung, Pohang University of Science and Technology, Pohang, South Korea
Abstract
The Virtual Pepper-Pot (VPP) is a 4D transverse phasespace measurement technique based on pepper-pot-like patterns that are generated by crossing each measured horizontal slit-based beamlet with all measured vertical slit-based
beamlets. The VPP beam phase space distribution reconstruction and simulation are performed using the Beam Delivery Simulation (BDSIM) code, which is a Geant4 toolkit.
The configuration includes a VPP 3D model slit, a scintillator screen, and a user-defined 1 MeV energy and 10 mAcurrent proton beam distribution, characteristic of the KOMAC RFQ beam test stand. Besides VPP, pepper-pot mask
simulation is carried out, and the intensity and emittancedifferences are observed. The input beam distribution is
generated from a TraceWin output file for comparison of
results. The comparison between the VPP analysis results
and the TraceWin input shows satisfactory results, ensuring
accurate estimation of the emittance.

INTRODUCTION
The measurement and analysis of transverse phase spacein particle beams are vital for optimizing accelerator performance and improving beam quality. Traditional techniques,
such as slit-based and pepper-pot methods, have been widelyused for these measurements. Besides these, the Virtual
Pepper-Pot (VPP) technique has been developed to achieve
high resolution and to provide fast scanning, offering a novel
approach to 4D transverse phase space measurements.
The VPP technique generates pepper-pot-like patterns
by crossing horizontal slit-based beamlets with verticalslit-based beamlets, providing a comprehensive view ofthe beam’s phase space distribution [1]. This method isimplemented using the Beam Delivery Simulation (BDSIM) code [2], a sophisticated simulation tool based on
the Geant4 [3] toolkit. BDSIM allows to simulate both thetransport of particles in an accelerator and their interaction
with the accelerator material.
A key application of the VPP technique is its use in the
Korea Multi-purpose Accelerator Complex (KOMAC) Radio
Frequency Quadrupole (RFQ) beam test stand. Here, a userdefined proton beam distribution with 1 MeV energy and
10 mA current is employed. The simulation configuration
includes a 3D model slit and a scintillator screen, considering
the main beam parameters of test stand.
To validate the VPP method, simulations are comparedwith traditional pepper-pot mask techniques. These compar-

isons focus on intensity and emittance differences, providing
insights into the advantages of VPP over conventional methods. Additionally, the input beam distribution is generated
from a TraceWin output file, allowing for a direct comparison between VPP analysis results and TraceWin inputs. The
satisfactory agreement between these results highlights theaccuracy and reliability of the VPP technique in estimating
emittance.
This paper aims to present a comprehensive overview
of the VPP technique, its construction, and its validation
through comparative analysis.

KOMAC BEAM TEST STAND LAYOUT
Radio-Frequency Quadrupole Beam Test Stand (BTS) isa proton accelerator structure at Korea Multipurpose Accelerator Complex (KOMAC) that accelerates beams to 1
MeV/n. In addition to the microwave ion source, an LEBT,
and an RFQ, the BTS consists of two beamlines, each withtriple quadrupole magnets and a wire scanner. A detailed
ion source extraction simulation study [4] shows that beams
are transmitted to LEBT with 25 keV energy and 10∼15 mAcurrent.
There are two beamlines at the KOMAC BTS, one ofwhich has a straight beamline (BL1) and another consistingof a bending magnet at 30∘ . Since the phase space measurement will be carried out BL1 in this study we will focus
on this beamline. The BL1 features four small quadrupoles
immediately after the RFQ and has a triplet quadrupole
structure to optimize beam transportation to the target chambers by adjusting the quadrupole gradients. The TraceWin
code [5] shows that the beam distribution from RFQ exit isfully transmitted to diagnostic chamber. Figure 1 gives the
RMS beam trajectories along the beamline, and the horizontal and vertical phase space distributions at the measurement
point are given in Fig. 2.

Figure 1: KOMAC BTS straight beam line envelope simulation. Blue line indicates 𝑥 axis while red shows 𝑦 axis.

∗ emrecosgun@unist.ac.kr

THPB095
808

THPB: Thursday Poster Session
MC1.1 Beam Dynamics, beam simulations, beam transport32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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CHROMATIC INDEX TO FIND A WORKING POINT FOR A 4TH
GENERATION SYNCHROTRON LIGHT SOURCE
E. Sánchez∗ ,1 , A. Flores-Tlalpa2 , J. Hernández-Cobos1 , M. Moreno3 , A. Antillón1
1
Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Morelos, México
2
Departamento de Bioingeniería y Ciencias, Tecnológico de Monterrey, Puebla, México
3
Instituto de Física, Universidad Nacional Autónoma de México, Cd. de México, México
Abstract
Optimizing the electron dynamics generated by MBA
cells involves adjusting a large number of parameters while
meeting complex constraints. These optimizations are typically performed using methods that involve calculating standard nonlinear functions, such as dynamic aperture. Thesemethods are often computationally expensive. Recently, aquasi-invariant surface technique for optimizing nonlinear
electron dynamics in storage rings has been reported. Building on this approach, a framework for optimizing the linear
parameters of a lattice without the need for particle tracking,or similar nonlinear calculations, is proposed. This framework enables the definition of the distorted chromatic index
𝜁𝐷,𝛿 , a valuable function for analyzing and tuning a cell
to identify a suitable working point for a machine. As an
example, these techniques are applied to identify a working
point for a ring model based on a 7BA cell, which comprises
20 cells and has a circumference of approximately 490 meters. After conducting nonlinear optimization, this approachachieves stable horizontal amplitudes exceeding 5 mm for
momentum deviations between −3% and 3%.

INTRODUCTION
Fourth-generation synchrotron light sources heavily rely
on MBA cells. However, controlling the complex electron
dynamics generated by these magnetic structures presents
significant challenges. For instance, adjusting numerous
parameters and meeting stringent constraints require sophisticated and computationally intensive tools. To addressthese challenges, various techniques are employed, including
global analyses of storage ring lattices [1], global optimizations of storage ring lattices [2], frequency map analysis [3],and the calculation of dynamic and momentum aperturesusing particle tracking [4, 5]. Additionally, methods such as
minimization of resonance driving terms [6–8] and hybrid
or unconventional approaches [9–14] are also used. However, to the best of our knowledge, there are few studies
focused on optimizing the linear designs of a cell [1, 2],
and no established protocols specifically address this type of
optimization without relying on typical nonlinear functions,such as dynamic aperture.
Recently, polynomial quasi-invariants of motion [15–18]
have been employed to optimize the nonlinear design of afourth-generation synchrotron light source storage ring [19].
This approach eliminates the need for particle tracking cal∗ esanchez@icf.unam.mx

THPB096812

culations, thereby reducing the reliance on costly computational resources. Here, we propose a framework that extend
this approach to optimize the linear parameters of a latticewithout requiring particle tracking or other similar nonlinear
calculations. This framework utilizes the distorted chromatic
index 𝜁𝐷,𝛿 , a valuable tool for analyzing and tuning a cell
to identify a suitable working point for a machine. As an
example, this technique is used to identify a working point
for a ring model based on a 7BA cell, which consists of 20
cells and has a circumference of approximately 490 meters.
Following nonlinear optimization, this approach enhances
the horizontal dynamics of the ring.

THE METHOD
The work in Ref. [6] demonstrates that a storage ring canbe modeled using a two-dimensional nonlinear Hamiltonianthat incorporates chromatic effects
1 2(𝑝 + 𝑝2𝑦 ) (1 − 𝛿 + 𝛿2 + ⋯) −2 𝑥
𝑏2 (𝑠)𝑏 (𝑠) 3𝑏 (𝑠) 2𝑏1 (𝑠) 𝑥 𝛿 + 1 𝑥 2 + 2(𝑥 − 𝑦2 ) + 3
(𝑥 −
2
2
3
𝑏 (𝑠) 43𝑥𝑦2 ) + 4(𝑥 − 6𝑥 2 𝑦2 + 𝑦4 ) + ⋯ ,(1)
4
𝐻(𝑥, 𝑝𝑥 , 𝑦, 𝑝𝑦 , 𝑠) =where the functions 𝑏1 (𝑠), 𝑏2 (𝑠), 𝑏3 (𝑠), and 𝑏4 (𝑠), are reΔ𝑝
lated to the magnetic field derivatives, and 𝛿 = 𝑝0 is the percentage deviation from the momentum 𝑝0 . A quasi-invariant
polynomial surface [18, 19] can be associated with this system. Up to order 𝛿2 , it can be written as follows
𝑆(𝑥, 𝑝𝑥 , 𝑦, 𝑝𝑦 , 𝛿) = 𝜎l + 𝜎nl + 𝜎𝛿1 𝛿 + 𝜎𝛿2 𝛿2 , (2)with 𝜎l , 𝜎nl , 𝜎𝛿1 and 𝜎𝛿2 its non-chromatic linear, nonchromatic nonlinear, first-order chromatic and second-orderchromatic contributions, respectively.
After substituting Eq. (2) into the invariance condition𝑑𝜕𝑆 = {𝑆, 𝐻} + 𝑆 = 0,
𝜕𝑠
𝑑𝑠

(3)

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ISSN: 2226-0366

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MICROSCOPIC UNDERSTANDING OF THE EFFECTS OF IMPURITIESIN LOW RRR SRF CAVITIES∗
K. Howard† , Y.-K. Kim, University of Chicago, Chicago, IL, USA
D. Bafia, Z. Sung, W. Dziedzic-Misiewicz, Fermi National Accelerator Laboratory, Batavia, IL, USA
Abstract
The SRF community has shown that introducing certain
impurities into high-purity niobium can improve quality
factors and accelerating gradients. We question why some
impurities improve RF performance while others hinder it.
The purpose of this study is to characterize the impurities of
niobium coupons with a low residual resistance ratio (RRR)
and correlate these impurities with the RF performance of
low RRR cavities so that the mechanism of impurity-based
improvements can be better understood and improved upon.
The combination of RF testing, temperature mapping, frequency vs temperature analysis, and materials studies reveals
a microscopic picture of why low RRR cavities experience
low BCS resistance behavior more prominently than theirhigh RRR counterparts. We evaluate how differences in themean free path, grain structure, and impurity profile affectRF performance. The results of this study have the potential to unlock a new understanding on SRF materials andenable the next generation of high Q/high gradient surface
treatments.

INTRODUCTION
As we approach the theoretical limit of niobium for superconducting radio-frequency (SRF) cavities, the last decade
has brought immense improvements in quality factor (Q0 )and accelerating gradients though intentionally added impurities into the niobium surface [1, 2]. Many SRF studies
follow a “clean bulk dirty surface” technique to optimize the
BCS resistance (RBCS ) by adding impurities to the surface
layer of high purity niobium such as nitrogen through Ndoping and oxygen through a low temperature bake [3–10].
The success of intentionally added impurities to the niobium surface has drawn deeper questions about how these
impurities affect cavity behavior, and has prompted an investigation of cavities with a low residual resistance ratio (RRR).
Low purity niobium has been studied previously for the purpose of cost reduction and possible high Q0 [11]. In thisstudy, we look at the intrinsic impurities as a resource to optimize the RBCS and understand the mechanism of impuritybased improvements. From the free electron model and the
Wiedemann-Franz law, RRR and mean free path (mfp) havea direct relationship 𝑙(𝑛𝑚) ≈ 2.13 ⋅ 𝑅𝑅𝑅 [12]. As a result,
we might expect to experience low RBCS behavior at low∗ This manuscript has been authored by Fermi Research Alliance, LLC

under Contract No. DE-AC02-07CH11359 with the U.S. Department ofEnergy, Office of Science, Office of High Energy Physics. This work was
supported by the University of Chicago.
† khoward99@uchicago.edu
THPB099816

RRR, as seen in Fig. 1. We ask if the intrinsic impurities canimprove performance, as we observe in extrinsic impurities.

Figure 1: A moderately dirty surface optimizes the BCS
resistance versus mean free path, adapted from [13].

RESULTS
Cavity Performance
In this study, we investigate a single-cell TESLA-shaped
1.3 GHz low RRR cavity in electropolished (EP) condition,
where the surface and bulk are uniform [14]. We measure
the Q0 at a given gradient by maintaining the cavity at its
resonant frequency, inputting power via antenna, and thenmeasuring the reflected and transmitted power [12]. We
compare the performance of the low RRR cavity to a high
RRR counterpart to understand how the intrinsic impurities
affect RF behavior. In Fig. 2, we observe the lower Q0 of the
low RRR cavity at all gradients, which is expected from theincreased dissipation and decreased thermal conductivity
from intrinsic impurities.
The surface resistance is the geometry factor divided by
Q0 . RBCS is the difference between the surface resistanceat 2 K and low temperature (< 1.5 K). This component represents the breakdown of cooper pairs with increasing temperature [3, 15]. In Fig. 3, we highlight the low RBCS of the
low RRR cavity. The low mfp of the low RRR material does
enable low RBCS since it is much closer to the optimal value,
recalling Fig. 1.

Material Characterization
We conduct a sample study using low RRR coupons cut
from the same sheet as the cavity to correlate the RF behavior
with the material properties. In EP condition, we measure
the ratio of the resistivity at room temperature to its residual
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32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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FABRICATION STATUS OF PRODUCTION SSR1 JACKETED CAVITIESFOR PIP-II AT FERMILAB∗
T. Aiazzi† , M. Parise, L. Grassellino, D. Passarelli, FNAL, Batavia, IL, USA
Abstract
This paper provides an overview of the current fabrication
status of superconducting SSR1 spoke cavities intended for
integration into the PIP-II SRF linac at Fermilab. It explores
the ongoing development and fabrication processes of thejacketed SSR1 cavity, highlighting key modifications madein the mechanical design to enhance structural integrity.

was observed in the endwalls, necessitating the addition ofreinforcing ribs.

Reinforcing Ribs
Four niobium ribs are welded to each endwall and connected to a reinforcing ring (Fig. 1).

INTRODUCTION
The Proton Improvement Plan II (PIP-II) project aims to
upgrade the accelerator complex at Fermilab to produce theworld’s most intense high-energy neutrino beam for the Deep
Underground Neutrino Experiment at the Long-Baseline
Neutrino Facility (LBNF). This upgrade includes the development of a linear particle accelerator with five typesof Superconducting Radio Frequency (SRF) cavities: HalfWave Resonator (HWR), Single-Spoke Resonator 1 (SSR1),
Single-Spoke Resonator 2 (SSR2), and low-beta and highbeta 650 MHz elliptical cavities (LB650 and HB650) [1].
Operating at 325 MHz, the SSR1 cryomodules will use
continuous wave RF power to accelerate H- beams from 10
MeV to 32 MeV (Table 1) [2]. The mechanical design of
the SSR1 cavities has been presented in an earlier work [3].
After finalizing the design by adding four reinforcement ribs
to the endwalls, the production of nine SSR1 cavities has
started. This paper presents the final design revision and thecurrent status of cavity fabrication and processing.

Figure 1: Welded reinforcing ribs.
The design accounts for both structural integrity and thefeasibility of the welding process. The cavity is engineered
to withstand an external Maximum Allowable Working Pressure (MAWP) of 0.205 MPa. At an operational temperatureof 2 K, this MAWP increases to 0.410 MPa. Additionally, aninternal pressure load up to 0.205 MPa, which could result
from helium leakage into the main volume during the warmup process, was also considered. The cavity has a tuning
range of 0.26 mm.

Table 1: Parameters of the SSR1 Cavity
Parameter

Value

Nominal Frequency
Target Frequency Allowable Error
MAWP @ RT
MAWP @ 2 K

325 MHz±50 kHz2.05 bar
4.1 bar

FINAL DESIGN REVISION
The structure of the bare cavity consists of four main
components Electron Beam (EB) welded together: the two
endwalls, the shell, and the spoke [4]. The endwalls are themost challenging components to form, and they are manufactured using the metal spinning technique. This techniqueprovides a more reliable forming process by minimizing
the risk of tearing, but it does result in a significant reduction in thickness. A maximum thickness reduction of 30%∗ This manuscript has been authored by Fermi Research Alliance, LLC

under Contract No. DE-AC02-07CH11359 with the U.S. Department ofEnergy, Office of Science, Office of High Energy Physics.
† taiazzi@fnal.gov
THPB100
820

Figure 2: Mechanical analysis of a SSR1 bare cavity without
ribs (left) vs with ribs (right).
The Fermilab ES&H manual mandates that the cavity be
rated for a MAWP in accordance with the relevant sectionsof the ASME Boiler and Pressure Vessel Code [5]. In compliance with Chapter VIII, Division 2 (Design by Analysis),several finite element analyses have been performed using
ANSYS [6] to determine the MAWP of the cavity, considering the reduced thickness of the endwalls and the additionof the reinforcing ribs. These analyses ensure that the cavity
THPB: Thursday Poster Session
MC3.7 Superconducting structures32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

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LONGITUDINAL BEAM DYNAMICS OPTIMIZATIONFOR INFRARED TERAHERTZ FEL LINAC
Y. M. Yang, S. C. Zhang, Z. G. He, G. Y. Feng†
University of Science and Technology of China, Hefei, China
Abstract
The high-repetition-rate infrared terahertz free-electron
laser (IR-THz FEL) facility is progressing in the preliminary research stage, which can achieve the demand for atunable high-power light source in the long wavelength
spectrum and form a complementary structure of advantages with the Hefei Advanced Light Facility (HALF).
In this paper, we present the design of a bunch compressor,
enabling compress the bunch length to reach the peak current of 118 A. We also introduce an approach to optimize
the RF parameters for the accelerating modules, whichmakes it feasible to generate a high-quality beam bunchthat can reach the requirements for future FEL applications.

INTRODUCTION
The paper introduces the design and optimization of ahigh-repetition-rate IR-THz FEL facility [1–4], which leverages optical resonator-based FEL technology to achievea higher mean power output by increasing pulse frequency.
Electron beam of the facility will be generated from a photocathode RF gun injector and further accelerated with asuperconducting linear accelerator. The C-type bending
magnet chicane is used to increase the peak current bycompressing the bunch length. During the beam dynamics
simulations, space charge effects, coherent synchrotron radiation (CSR) effects and longitudinal cavity wake field effects have been taken into account with the codes of ASTRA [5] and CSRTrack [6].

LAYOUT
The schematic layout of the IR-THz FEL facility isshown in Fig. 1. The injector consists of a photocathodeRF gun, an L-band accelerating section and a third-harmonic accelerating section. The electron bunches are generated by using a normal conducting 1.3 GHz RF gun.

reaching 5 MeV [7-8]. After the gun, the electron bunches
are accelerated in a superconducting 9-cell TESLA cavity [9] with resonant frequency of 1.3 GHz: ACC1. Downstream of the ACC1 section, a third-harmonic RF system [10,11], operating at 3.9 GHz and referred to as
ACC39, will be used to linearize the longitudinal phasespace distribution with RF curvature distortion and to minimize the bunch tails in the subsequent chicane. The electron beam energy is 20 MeV at the exit of ACC39 section.
There is a bunch compressor chicane (BC) with a C-type
structure downstream of the ACC39 section. The beam energy is increased to 58 MeV after passing through the main
linac, which is equipped with two L-band superconducting
9-cell TESLA cavities, named ACC2.
The IR-THz FEL will operate in the oscillator mode,
which generates FEL radiation with wavelengths ranging
from 5 μm to 1000 μm. After the ACC1 section, electron
bunches are deflected to the undulator (U1) by a beam distribution system, and THz radiation with wavelength rangeof 200–1000 μm can be generated in the U1. Following the
ACC2 section, the electron bunches are distributed into
two distinct undulators, which generate mid-infrared(5–40 μm) and far-infrared (40–200 μm) radiation respectively.

BUNCH COMPRESSION
The linac-based free-electron laser require very shortbunches of high-brightness electron beams with high peakcurrents. The bunches cannot be directly generated in rfgun, as space charge forces would result in the deterioration of the beam quality in a short distance. Therefore, electron bunches must start with a low intensity and a few tensof Amperes peak current, and subsequently be accelerated
to energy where the space charge effects are sufficiently
weakened. In this case, the peak current can be increased
by compressing the bunch length.

Figure 1: The schematic layout of the IR-THz FEL facility.
_____________________________________________________* Work supported by Supported by the Hundred-person Program of Chinese Academy of Sciences†
fenggy@ustc.edu.cn
THPB101824

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ISBN: 978-3-95450-219-6

ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-THPB102

T. Banaszkiewicz∗ , M. Chorowski, P. Duda, M. Stanclik
Wroclaw University of Science and Technology, Wroclaw, Poland
R. Dhuley, A. Martinez, W. Soyars, Fermi National Accelerator Laboratory, Batavia, USA
Abstract
The PIP-II linac Cryogenic Distribution System (CDS)
is characterized by extremely small heat inflows and robust
mechanical design. It consists of a Distribution Valve Box(DVB), Intermediate Transfer Line, Tunnel Transfer Line,
comprising 25 Bayonet Cans, and ends with a TurnaroundCan. Multiple helium streams, each characterized by distinct
helium parameters, flow through each of these elements. The
CDS geometry allows maintaining an acceptable pressure
drop for each helium stream, considering the planned flows
and helium parameters in different operation modes. Thisis particularly crucial for the return line of helium vapors,
which return from cryomodules to the cold compressors andthus have very restrictive pressure drop requirements. On
both sides of the DVB there are fixed supports for process
pipes. One of the DVB design challenges was to route theprocess pipes in such a way that their shape provided sufficient compensation for thermal shrinkage. This ensures thatthe forces resulting from thermal shrinkage acting on the
cryogenic valves remain at a level acceptable to the manufacturer. The required thermal budget of the CDS was achievedby thermo-mechanical optimization of its components, likeprocess pipes fixed supports in Bayonet Cans.

PIP-II CDS OVERVIEWThe Cryogenic Distribution System is tasked with providing cooling power from the cryogenic plant to the linear
accelerator (linac) cryomodules. The simplified layout of
the CDS is shown in Fig. 1.
Warm helium supply

Cryogenic
Plant

HTTS Return
HTTS supply
LTTS Return
4.5 K Supply
2 K Return line
CD Return line

Low pressure suction

Intermediate
Transfer LineU-tubes

Vent header

Cavity string

Phase

separator
TunnelTurnaround
Transfer LineCan
& Bayonet Can

The linac consists of five distinct types of cryomodules,
each of which is connected to the CDS via its own dismountable, bayonet connection for each process line. The CDS∗ tomasz.banaszkiewicz@pwr.edu.pl

828

PRESSURE DROP
The first discussed challenge was designing the heliumtransfer line and the helium branched lines in such a way
as to meet the constraints of allowable pressure drop budgets. Special attention was given to the helium vapor returnline from the cryomodules (2 K Return line). This is a vacuum line used to return the evaporated helium stream fromthe cryomodules to the cold compressors located in the cryoplant building. During the design of the process lines, alloperational modes had to be considered, from the cool-downof the installation through the nominal operating mode to
emergency modes. Examples of the helium stream requirements in the nominal operating state and the corresponding
pressure drop budget requirements are shown in Table 1.

CDS circuit

Press. drop budget

Mass flow

HTTS
4.5 K Supply
LTTS Return
2 K Return

280 mbar
30 mbar
30 mbar
4.3 mbar≥ 65 g/s≥ 172 g/s
≥ 25 g/s≥ 147 g/s

Cryomodule

Figure 1: PIP-II CDS layout.

THPB102spans approximately 285 meters, running from the Distribution Valve Box at the cryogenic plant interface, throughtwenty-five Bayonet Cans which are the points where themain helium stream branches into streams that supply the
cryomodules, to the Turnaround Can at the linac’s end.
The CDS process circuits with size of the main and thebranch line and nominal operating conditions (temperaturesand pressures) are:• 4.5 K Supply - DN50/DN15 at 4.5 K and 2.9 bara
• 2 K Return - DN250/DN65 at 3.8 K and 3.1 mbara• Low Temperature Thermal Shield Return (LTTS)DN50/DN15 at 9 K and 2.9 bara
• High Temperature Thermal Shield Supply (HTTS-S) DN50/DN20 at 40 K and 18 bara
• High Temperature Thermal Shield Return (HTTS-R) DN50/DN20 at 80 K and 18 bara
• Cooldown Return (CD) - DN80/DN20 at 80 K

Table 1: CDS Process Circuit Pressure Drop Budget

Distribution Valve Box

CMrelief line

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PIP-II LINAC CRYOGENIC DISTRIBUTION SYSTEMDESIGN CHALLENGES

The calculations considered all influences on the pressure drop due to the geometry of the individual process
circuits, including straight sections, elbows, tees, constrictions, valves, etc. Additionally, geometric constraints related
to the actual placement of the individual system elements
were taken into account in the calculations. For example,
THPB: Thursday Poster Session
MC4.2 Cryomodules and cryogenics

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-FRXA001

H. Hähnel1,2† , A. Ateş1 , B. Dedić1 , J. Kaiser1,2 , C. Wagner1 , U. Ratzinger1,21Institute of Applied Physics, Goethe University, Frankfurt a. M., Germany
2
Helmholtz Forschungsakademie Hessen für FAIR (HFHF), Frankfurt a. M., Germany
Abstract
Additive manufacturing (AM) has become a powerful tool
for rapid prototyping and manufacturing of complex geometries. A 433 MHz IH-DTL cavity has been constructed toact as a proof of concept for direct additive manufacturingof linac components. In this case, the internal drift tube
structure has been produced from 1.4404 stainless steel, as
well as pure copper using AM. We present the most recent
results from high power tests with the AM IH-type structure.

INTRODUCTION
A prototype IH-type cavity was constructed as the basis
for a proof of concept of additive manufacturing for the
production of linac structures (see Fig. 1). The cavity isdesigned to operate at 433.632 MHz and to provide a total
acceleration voltage of 1 MV to a 1.4 MeV proton beam.
The inner length of the cavity on the beam axis is 146 mm,
resulting in an effective acceleration gradient of 6.8 MV/m
at full design power [1–3]. AM of stainless steel stems
or drifttubes with CNC postprocessing and copper plating
has been implemented in some projects already [4, 5]. A
recent focus of AM research for linac production has been
production of pure copper parts [6–10]. In this paper we
present first high power RF tests up to 25 kW, 5 MV/m witha 3D printed copper linac structure.

Figure 2: Top view of the assembled prototype cavity with
AM copper girders mounted. (AM copper components got
a surface finish by CNC controlled milling.)
be tested. The inside of the test cavity was copper plated andis sealed by an aluminum wire backed by a pre-vacuum ando-ring (see Fig. 2). At the mount-point of the 3D printed
drifttube structure, a similar vacuum seal with a pre-vacuum
backed aluminum wire is performed interfacing directly on
the printed part. Using this concept, reliable vacuum pressures around 1 × 10−7 mbar were achieved using stainlesssteel, as well as copper AM parts [2]. Due to its modular
design and precision mounting points for the drifttube structures, multiple 3D printed structures could be tested in thiscavity.

Printed Parts

Figure 1: Printed copper parts after CNC post-processing(left) and cross-section of the cavity geometry (right).

EXPERIMENTAL SETUP
For the prototype, a stainless steel cavity was manufactured to house AM produced girder-drifttube structures to∗ Work supported by BMBF 05P21RFRB2† haehnel@iap.uni-frankfurt.de

FRXA: Main Session FRX
MC3.6 Room temperature structures

To date, three different revisions of the drifttube structure
were designed and printed from stainless steel and finallypure copper. The current revision features cooling channels
running through the girder and up to just below the drifttubes.
AM copper parts after manufacturing have a surface roughness in the order of 𝑅𝑧 = 15−30 µm. Therefore, for firsttests with these structures, the contour of the parts was CNC
machined to remove 200 µm from all surfaces, providing anear mirror finish on the flat sides (see Fig. 1). Additionally, the sealing surfaces for the vacuum und water seals
on the bottom of the printed part also have to be machined.
In future investigations, the focus will be on achieving thesame performance by utilizing surface polishing techniques
to reduce the complexity of part manufacturing.

RF Coupler
Due to the small dimensions of the cavity and the largest
flange size being CF40, a compact RF coupler had to be
developed for high power RF tests. A first revision without
any active cooling [2] was used for first low power condiFRXA001
831

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HIGH POWER TESTS OF AN ADDITIVE MANUFACTURING IH-TYPE
CAVITY∗32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-FRXA003

SRF COAXIAL RESONATORS FOR HADRON ACCELERATION

Abstract
SRF technology using niobium accelerating cavities enables high performance and efficient acceleration for modern accelerator projects. While electron LINACs accelerateparticles with common structures designed for relativistic
acceleration, hadron LINACs require acceleration over abroad velocity range. SRF technology is now being adopted
at hadron energies in some cases starting from the RFQ exit
but with top end energies such that a velocity range of a factor of ten has to be considered in the LINACs configurationand cavity design. Different structures in the TEM mode
(coaxial) class (QWR, HWR, SSR, DSR) are employed withcustomized rf frequency, design beta and cavity structure.
The coaxial cavities are now operating at very high performance rivaling the achievements in the 1.3 GHz ellipticalcavities. This paper gives an overview of the state of the artof usage of coaxial cavities and highlights research on theperformance of these cavities.

practical for velocities of 𝛽 > 0.6, the community relies on
different variations of TEM mode coaxial resonators (quarter wave resonators (QWR) for 𝛽 < 0.15 and half wave
resonators (HWR) and single or double spoke resonators(SSR, DSR) for higher velocities) to span the ‘low 𝛽’ velocity range. As the longitudinal emittance scales as 1/(𝛽𝛾),cavities in the lower velocity range require lower frequencies to provide sufficient longitudinal acceptance favouring
QWRs near 100 MHz with HWRs adopted for f ∼ 200 MHz
and SSRs around f ∼ 300 MHz. The RF surface resistance
𝑅𝑠 is inversely proportional to the quality factor 𝑄 0 and forsuperconducting cavities follows
𝑅𝑠 = 𝑅 𝐵𝐶𝑆 (𝑇) + 𝑅res ,(1)with 𝑅res as a temperature independent residual resistanceand 𝑅 𝐵𝐶𝑆 as temperature dependent resistance, which canbe approximated [6] as
𝐴 2 − 𝑘 Δ𝑇𝜔 𝑒 𝑏 ,
(2)𝑇with 𝐴 as a material properties constant, 𝑇 as temperature, 𝜔as rf frequency and Δ as superconducting gap. The quadraticincrease in 𝑅BCS with 𝜔 means that lower frequency cavities
like QWRs and HWRs can be operated near atmosphericpressure liquid helium (T∼ 4.2 K) while higher frequency
cavities usually adopt operation below the 𝜆 point at 𝑇 = 2 K.
Since the gap structure of a coaxial cavity is proportional
to 𝛽𝜆 and the transverse dimensions are proportional to 𝜆, thelow 𝛽 coaxial cavities have necessarily more compressed geometries than elliptical cavities with larger ratios of 𝐵 𝑝 /𝐸 acc
and 𝐸 𝑝 /𝐸 acc . This results in lower accelerating gradientscompared to 𝛽 = 1 elliptical cavities but performances of
coaxial resonators are now rivaling those reached in ellipticalresonators in terms of achieved 𝐵 𝑝 and 𝐸 𝑝 .
Much of the SRF performance research has focused on
the elliptical 1.3 GHz 𝛽 = 1 cavity as the same cavity is used
100’s to 1000’s of times in many different projects worldwide. Developments include both efforts to increase 𝑄 0 and𝐸 acc to lower operating costs and decrease capital costs. On
the other hand, for hadron accelerators, cavity designs are
typically project specific with a few unique cavity types tocover the required velocity range. This makes dedicated performance research and development challenging to transfer
between labs. Nonetheless there is a strong need for improved performance of TEM mode cavities as more hadron
accelerators using SRF cavities come online. Not only high𝑄 0 and high 𝐸 acc are important topics for these accelerators,
but also maintaining performance and reliability.
This paper will discuss the current landscape of SRF based
hadron accelerators and showcase individual R&D, as wellas covering dedicated, purpose-built research cavities fromTRIUMF and JLab.
𝑅BCS =INTRODUCTION
Superconducting radio-frequency (SRF) cavities allow
particle acceleration at high gradients in continuous wave(cw) operation due to the low surface resistance 𝑅𝑠 andresulting high quality factors 𝑄 0 . Over the past years, performance of SRF cavities have increased significantly. Both𝑄 0 and accelerating gradients 𝐸 acc have been increased due
to improved surface preparation and novel heat treatmentsof the niobium material. Conventional treatments like the120 ◦ C/48hr vacuum bake result in a relatively constant 𝑄 0
as a function of accelerating field, while new treatments likeN2-doping [1] and O2 diffusion [2] result in 𝑄 0 ’s that risewith increasing 𝐸 acc .
These new treatments were discovered using elliptical
1.3 GHz cavities operating at 2 K, which are the typicalchoice of cavity for 𝑒 − accelerators, such as EU-XFEL [3],LCLS-II [4], and SHINE [5]. While the gradient 𝐸 acc defines the accelerating performance, SRF cavity performanceis bounded by the peak magnetic and electric rf fields atthe cavity surface 𝐵 𝑝 and 𝐸 𝑝 . Nine-cell 1.3 GHz ellipticalcavities used in pulsed, high gradient applications routinely
reach accelerating gradients 𝐸 acc of 30 MV/m, which corresponds to peak surface magnetic fields 𝐵 𝑝 of 120 mT andelectric surface fields of 60 MV/m. Performance of continuous wave (CW) electron linacs (LCLS-II) are specified
at gradients near 20 MV/m corresponding to 𝐵 𝑝 values of
80 mT and 𝐸 𝑝 = 40 MV/m. As will be summarized in thenext section, a new generation of large hadron LINACs are
now being realized or developed with SRF sections startingat energies of a few MeV/u (ie 𝛽 ∼ 0.06) and extending
to near relativistic energies. As elliptical cavities are only
∗ kolb@triumf.ca

FRXA: Main Session FRX
MC4.8 Superconducting RF

FRXA003
835

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P. Kolb∗ , R. E. Laxdal, TRIUMF, Vancouver, B.C., Canada

32nd Linear Accelerator Conference (LINAC2024),Chicago, IL, USA
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ISSN: 2226-0366

JACoW Publishingdoi: 10.18429/JACoW-LINAC2024-FRXA004

E. Sargsyan*, A. M. Lombardi, G. Bellodi, J.-B. Lallement, P. K. Skowronski, R. Wegner
CERN, Geneva, Switzerland
Abstract
Since its completion in 2017, Linac4, the new 160 MeV
proton injector for the CERN accelerator complex, has undergone some tests to assess and improve reliability, until
being connected to the Proton Synchrotron Booster (PSB)
during the 2018–2020 Long Shutdown 2 (LS2). The performance requirements for the LHC high-luminosity upgrade have been successfully met, and during its first threecomplete years of operation the linac has shown high reliability figures. Recent improvements of the H- ion source
enable the increase of the beam current from the nominal
35 mA to 50 mA, opening the possibility for increasing theintensity of the Booster beams, for the benefit of the experimental programmes. This paper presents the operational
experience and reliability of Linac4 in its first three yearsof operation.

INTRODUCTION
Linac4 [1] is a normal conducting linac consisting of a
45 keV caesiated RF H- ion source, Low Energy BeamTransport (LEBT), 3 MeV Radio Frequency Quadrupole(RFQ), Medium Energy Beam Transport (MEBT) with achopper and 3 bunching cavities, 3 Drift Tube Linac (DTL)
tanks up to 50 MeV, 7 Cell-Coupled DTL (CCDTL) modules up to 102 MeV, 12 Pi-Mode Structure (PIMS) cavities
up to 160 MeV, and 1 de-buncher cavity, all resonating at
352.2 MHz. The chopper modulates the beam pulse time
structure to reduce beam losses during the beam capture
process in the Proton Synchrotron Booster (PSB) and whenswitching between its 4 rings. The peak beam current fromthe source is 35 mA, resulting in 27 mA out of the RFQ and
25 mA at the PSB injection with shot-to-shot modulated
pulse length of 0–600 μs at 0.83 Hz repetition rate. Linac4
became the injector of the CERN proton accelerator complex in 2020, replacing the 50 MeV Linac2 after 40 yearsof service. Providing 160 MeV H- ions, it has been the firststep of the LHC Injectors Upgrade (LIU) project [2], implementing a charge exchange injection process and doubling the PSB injected intensity, resulting in a luminosity
increase in the LHC injector chain. The commissioning
staged in beam energy steps started in 2013, reaching its
final beam energy in 2016. Several reliability and performance improvement runs took place [3], until it was finallyconnected to the PSB. Since then, Linac4 performance andreliability were continuously analysed and improved.

OPERATIONAL EXPERIENCE

according to the plan [4]. The PSB beam brightness goal
was quickly reached and even surpassed [5]. The experience from the first year of Linac4 operation is described in[6, 7]. The achieved beam performance is within the specifications [6]. The normalized rms emittance measured at
the PSB injection is 0.26 𝜋.mm.mrad in both transverse
planes (the requirement is 0.4 𝜋.mm.mrad for a 40 mA
beam current). The measured optics mismatch factor(Eq. 7.98 in [8]) was 0.08. The pulse flatness in terms ofbunch position and energy are one of the key parameters.
The beam loading effect in the cavities is compensated by
feedback and adaptive feedforward (AFF) systems operating concurrently. When the pulse length or chopping factor
are changed, the feedforward correction is automatically
reset, while feedback is kept active. By observing deviations in the measured cavity amplitudes and phases fromthe requested values, AFF develops corrective waveforms
that are applied on the subsequent pulse of the same type.
This permits to achieve smaller than 10 keV energy deviations at the PSB injection.
The pulse position stability in the horizontal plane is wellwithin the specified 1 mm. In the worst case, it is measured
to be 0.4 mm and the deviation is visible only for the very
first couple of microseconds. On the other hand, in the vertical plane it is slightly above 1 mm, and the slope is visible
all along the pulse. The most likely reason is the 3 MeV
chopper voltage.
The pulse-to-pulse beam stability in terms of intensity,
position, and energy deviations is within the defined margins of 2%, 1.5 mm and 100 keV, respectively. A feedback
system keeps the measured beam intensity in the LEBT
constant by regulating the amplitude of the 2 MHz RF
power of the source [9]. This system is also capable of automatically adjusting the intensity in the MEBT; however,
it is not enabled for operational beams because no drift in
the RFQ transmission was ever observed.
A dedicated web service (Beam Performance Tracking)was developed at CERN that provides plots showing evolution of the key accelerator parameters [10]. For Linac4,
it shows plots of beam intensity, transmission, position, andphase for the past week for each beam user. The RF amplitudes and phases are plotted for the past 60 days. Resultsof various statistical analyses are also made available. This
helps to monitor the machine status and to detect problems
with the machine stability.

Startup, Commissioning, and Operation* edgar.sargsyan@cern.ch

Linac4 yearly operation typically starts in March after
the beam re-commissioning, when the beam is sent to the
PSB, and ends in November, when a year-end technicalstop starts to allow for maintenance of the accelerator complex. During the first week after the end of the run, experts

FRXA: Main Session FRXFRXA004

In Dec. 2020, the beam was sent to the PSB for the firsttime. The charge exchange injection was commissioned___________________________________________

MC3.5 RFQs

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OPERATIONAL EXPERIENCE AND RELIABILITY
OF THE NEW CERN LINAC4